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View Full Version : 1990 Tristar hesitation/backfire


hairlesshacker
09-14-2013, 12:19 AM
So my 90 tristar (351w) is acting up again...

First of all, it's been hard to start since I renewed the carb last year. If I floor it twice before cranking, it will start every time. I know with a carb engine you have to do this when it's cold. But I mean even after it's been pulling the kids around the lake for an hour. Stop the engine while they climb back in, and it won't start unless I first pump the throttle once or twice (prior to turning the key) to get a good squirt from the accelerator pump... It used to start with just a turn of the key.
I can live with this, but it may be related to my real problem...

This past weekend after puling the kids for a few hours, it started to glass off, so my wife wanted to ski..
She said hit it, and as soon as I tried to pull her up, the engine stumbled and backfired.
Of course I dragged her underwater a bit, she cursed me, said "hit it" again, and I pulled her up a bit more gradually, and away we went..

I was up next, and of course when she went to pull me, it did the same thing. Backfire, stumble, face full of water for me. After a few tries she managed to pull me up...

It idles ok, pulls the kneeboarders OK, but when I try to get on it with a load (anytime I pull a slalom skiier), it wants to stumble/hesitate and sometimes backfire.

So.. what should I be looking at?

I double checked the timing, it's at 10 degrees. Not sure about advance, I looked under the EI rotor, the weights and such look OK, but one spring is definitely not right (somebody must have replaced it) and it's too big, not doing anything. But the other spring is good, and if I push them out, they spring right back. I know I need to fix this, but this has been this way for the 7 yrs I've owned it, so I don't think it's the problem? (surprised I didn't notice when I switched out to EI last year though.)

I guess I just don't know if I should be suspecting the carb or the ignition or a head gasket or something else..

hairlesshacker
09-18-2013, 11:43 PM
Took it back out to the lake last weekend, and spent a little more time trying to see what was going on....
I found that it stumbles/backfires any time you accelerate quickly from idle. If I start from idle, and get on it, it will pretty much stumble/stall and possibly backfire every time. (I think it's through the carb, not the exhaust, so maybe backfire isn't the right term?) If I accelerate slowly/gradually, it's fine.

(Good news is it still pulled well enough for the kids to board, and I even got a good ski run in.. My 8yr old mastered getting up on the wakeskate, and my 4 yr old has the skis and kneeboard all figured out.. )

Anyhow, back to the issue....
So I did a compression test. They were pretty much all at 135 psi +/- 5.
So I think I'm OK there...

One thing I noticed when warming up the engine before the test is that the right side exhaust riser was warmer than the left side. Both were still cool enough to touch, but one was noticeably warmer. All the plugs looked OK, so I'm pretty confident they're all firing... A few weeks ago the engine was running hot, so I changed out the impeller.. The old one was pretty chewed up, so I'm sure I've got some pieces of impeller clogging the water flow. I don't think this would be the cause of the hesitation/backfire though?

I got a new distributor cap, since the existing one is at least 7yrs old, and possibly 23. It looks OK though, so I don't think that's the issue.. Don't have new springs for the advance weights yet.. Anyone know the source for those? Certainly need to replace them...

I guess the next thing I'll check is the float levels, maybe I got them too low when redoing the carb....
And I guess I'll probably try to check for vacuum leaks/intake leaks...

Any other ideas of what I should be looking at?

(I don't really know what I'm doing, but I hate to pay someone 100 bucks an hour that won't necessarily fix it either... Last time I paid a dealer 500+ to fix it, they rebuilt the carb, but didn't check the filter on/under the fuel pump.. They didn't fix the issue, and when I figured it out (by reading this forum), I found that filter to be rusted and disintegrated. Called the dealer and they said "we didn't know there was a filter there, that's a really old boat"... Since then I've tried to educate myself and do my own maintenance..)

thatsmrmastercraft
09-19-2013, 12:06 AM
Sounds like you are doing things right so far. Possible sources for hesitation/backfire upon hard acceleration are from both fuel and/or ignition.

Fuel possibilities:
Accelerator pump insufficient volume
Accelerator pump nozzles clogged
Accelerator pump stroke not set correctly
Choke not opening fully
Significant vacuum leak

Ignition Possibilities:
Spark plugs - replaced
Spark plug/coil wires
Distributor cap & rotor - cap replaced (what about rotor?)
Timing - confirmed
Distributor advance - if your advance weights don't come back to base timing, or advance too quickly, you will have too much advance causing described problem

hairlesshacker
09-19-2013, 01:18 AM
Fuel possibilities:
Accelerator pump insufficient volume
Accelerator pump nozzles clogged
Accelerator pump stroke not set correctly
Choke not opening fully
Significant vacuum leak

So I have checked the accelerator pump, it seems to have a steady stream when I move the throttle.. I don't believe the renew kit came with a new nozzle; I think the one I have now is the same one I've always had. Not sure about the stroke, I attempted to adjust this per holley's tutorial to make sure it had the right clearance so it wasn't pushing the lever too far. Verified the choke is opening fully, it is functioning correctly. Also idled the boat and turned the two idle mixture screws in all the way (following holley's instructions for checking the power valve). Engine died as expected. Does this also rule out vaccum leak? I used the vac guage when setting the carb mix, but don't really know how to check for a leak. I guess spray around base of the carb with starting spray to see if idle goes up? I think there's only one vaccum hose, from base of carb to PCV...


Ignition Possibilities:
Spark plugs - replaced
Spark plug/coil wires
Distributor cap & rotor - cap replaced (what about rotor?)
Timing - confirmed
Distributor advance - if your advance weights don't come back to base timing, or advance too quickly, you will have too much advance causing described problem

I didn't replace the plugs this spring, because they were pretty new and looked good, but I put new ones in today after doing the compression test.. I replaced the plug and coil wires last week.
I got the new distributor cap in the mail today; will put it on tomorrow. The rotor is fairly new, it came with the EI kit I installed last summer.

The advance springs certainly aren't right... One spring looks too big, it looks like it's not the right spring, and doesn't fit right, it is loose. If I pull the weights out, they snap right back, but it seems like only one spring is really doing the work. I've checked the base timing many times, so I think it's coming back OK. Perhaps with only one spring it advancing faster than it should.

I don't know where to get the right springs -- didn't see them at skidim.
Maybe these would work? http://www.jegs.com/i/Mr.+Gasket/720/925D/10002/-1

hairlesshacker
09-19-2013, 01:33 AM
Well, maybe I'm making a bad assumption, I thought the two springs should look identical... :confused:
Mine are not.

But then I see this pertronix part, which looks like two different springs, this might be what's on mine... I'll have to look closer tomorrow.

http://www.summitracing.com/parts/pnx-018-1001/overview/

http://static.summitracing.com/global/images/prod/mediumlarge/pnx-018-1001_ml.jpg

drschemel
09-19-2013, 10:09 AM
Doesn't seem like it would be the dizzy as the spark advance does not occur at the low RPM's that you would have when you first hit the throttle. You can disconnect the vacuum advance and recheck your timing to make sure it is starting at the right place. Then reconnect and check to see if you are getting adequate advance at higher RPM's.
I think I would concentrate on the spark. Possibly the coil is getting weak and not hot enough to fire effectvely when you flood the cyclinders with fuel. Also wouldn't hurt to clean and regap the spark plugs. Are your ignition wires old? You might be loosing voltage there.
The nice thing about these older motors is no computer to mess things up, but then again, it also means you have to trouble shoot the fuel and ignition systems manually!

ccelia
09-19-2013, 10:17 AM
I had a very similar issue with my 89 prostar. I ended up replacing the carb, fuel pump, fuel filter, fuel/water separator, plugs, distributor, cap, rotors and the issue of falling flat on its face was still there.

I found that the vent line for the gas tank was clogged, so I wasn't getting the proper fuel to the carb. The boat ran and idled fine, but when I went to hit it, I got nothing. Also, check the fuel lines as well as the anti-syphon valve (they can stick from time to time).

hairlesshacker
09-19-2013, 10:18 AM
It's a marine distributor, there's no vacuum advance.
I know there shouldn't be advance at those RPMs, I think the theory was it could possibly be advancing too soon because the springs weren't right.

thatsmrmastercraft
09-19-2013, 10:21 AM
Doesn't seem like it would be the dizzy as the spark advance does not occur at the low RPM's that you would have when you first hit the throttle. You can disconnect the vacuum advance and recheck your timing to make sure it is starting at the right place. Then reconnect and check to see if you are getting adequate advance at higher RPM's.
I think I would concentrate on the spark. Possibly the coil is getting weak and not hot enough to fire effectvely when you flood the cyclinders with fuel. Also wouldn't hurt to clean and regap the spark plugs. Are your ignition wires old? You might be loosing voltage there.
The nice thing about these older motors is no computer to mess things up, but then again, it also means you have to trouble shoot the fuel and ignition systems manually!

there is no vacuum advance on a marine distributor......just sayin';)

thatsmrmastercraft
09-19-2013, 10:24 AM
It's a marine distributor, there's no vacuum advance.
I know there shouldn't be advance at those RPMs, I think the theory was it could possibly be advancing too soon because the springs weren't right.

You beat me to it.

Have you looked at the fuel stream provided by the accelerator pump? Should be a nice clean stream. Obviously do this with the engine off.

I would also look for vacuum leaks by spraying around the carb base and intake manifold with carb cleaner.

drschemel
09-19-2013, 02:39 PM
there is no vacuum advance on a marine distributor......just sayin';)

OK, my bad! I guess I never looked that close at it.

thatsmrmastercraft
09-19-2013, 02:41 PM
OK, my bad! I guess I never looked that close at it.

No big deal.

j.mccreight@hotmail.com
09-19-2013, 09:33 PM
...........

hairlesshacker
09-19-2013, 09:58 PM
I found that the vent line for the gas tank was clogged, so I wasn't getting the proper fuel to the carb. The boat ran and idled fine, but when I went to hit it, I got nothing. Also, check the fuel lines as well as the anti-syphon valve

I don't think my vent line is clogged, because every time I fill it with gas, it squirts gas out the vent.

I checked the anti-siphon valve on the tank a couple of years back and it was good, so I doubt it's gummed up since then, but I might as well check it...

However, my fuel hoses may need to be replaced. They look good, but as far as I can tell they are original (they say 1989 on them).


I put the new distributor cap on today, and checked on the advance springs.. Anybody know if this is right? One is a weaker spring, but is taught. The other is a stronger spring, but has play in it so it doesn't engage until the weights are almost all the way out. It does snap back to center as expected.. I'm guessing these are original? I had assumed the two springs would be identical, but I have no clue...:confused:

http://i.imgur.com/qoCcOR0.jpghttp://i.imgur.com/htoTKq3.jpghttp://i.imgur.com/4fipxbT.jpg

j.mccreight@hotmail.com
09-19-2013, 10:32 PM
I don't think my vent line is clogged, because every time I fill it with gas, it squirts gas out the vent.

I checked the anti-siphon valve on the tank a couple of years back and it was good, so I doubt it's gummed up since then, but I might as well check it...

However, my fuel hoses may need to be replaced. They look good, but as far as I can tell they are original (they say 1989 on them).


I put the new distributor cap on today, and checked on the advance springs.. Anybody know if this is right? One is a weaker spring, but is taught. The other is a stronger spring, but has play in it so it doesn't engage until the weights are almost all the way out. It does snap back to center as expected.. I'm guessing these are original? I had assumed the two springs would be identical, but I have no clue...:confused:

http://i.imgur.com/qoCcOR0.jpghttp://i.imgur.com/htoTKq3.jpghttp://i.imgur.com/4fipxbT.jpg

The Prestolite uses a two stage systems with a heavy and a flyweight spring, utilizing the flyweight for low rpm operation and then the heavier spring takes over for high rpm operation. What you need to do is to check the spring operation is to use an advance timing light to ensure smooth timing advance, usually around 26-30 of total timing around 3000 rpms on a stock setup. If the timing is not smooth or the engine doesn't reach mid-high 20 of total timing the springs could be sprung. If this is your case you are SOL as replacements are not available. The automotive springs will just make you pull your hair out, there was a company on ebay selling nos prestolite distributors over the summer but I think they sold out. I would recommend a mallory distributor as a replacement, however petronix is cheaper, I have no experience with petronix just with mallory and I see quite a few threads about bad petronix so you do your own research. This is the mallory that I used http://www.summitracing.com/parts/maa-9-26501, abit pricey but it's has been a great unit, they do make points style and different electronic versions.

hairlesshacker
09-19-2013, 10:56 PM
j.mccreight - Thanks for the info on the springs, that's what I needed to know...

I don't think the advance is the problem, I was just looking at that because I didn't realize it should be two different springs.. So thanks for confirming that is the correct original setup.

I don't have an advance timing light, just the el-cheapo one from harbor freight...

Even if this isn't advancing right, I don't think this is the cause of my problems... I don't think I'm even getting to 1500 RPM when it dies on me, so I don't think it would be advancing much yet.

And it seems to do Ok when I accelerate slowly to over 3000. It's only sudden acceleration that's an issue.
and seems to be mostly an issue if I've been sitting at idle for a minute, and then try to gun it.

pbgbottle
09-30-2013, 12:14 AM
Have you tried putting the points back in it I had the same problem after rebuilding carb and switching to pertronix EI.
Switched back to the points and problem was gone Also look down the carb after u shut down the engine and check for fuel dripping out of the boosters. Mine was dripping fuel also after shutting down the motor which also was causing problems. Once I got the carb dialed in I tried the EI again and it started acting up again. Just something for u to check and think about.


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hairlesshacker
10-06-2013, 04:37 PM
So I took it out two weeks ago after replacing the distributor cap.
It was running terribly, until I figured out that after the compression test, I let my family assist with replacing the plug wires, and several of them weren't seated correctly. After I pushed them on good, it was back to how it was before (idling fine, still having trouble on accel)

I also checked for vacuum leak by spraying wd40 around the base of the carb, but didn't find anything..

We had my sister-in-law with us, so the family wasn't very patient with me messing the engine, they just wanted to play... Put on the barefoot boom and taught sis-in-law to wakeboard. Then I took a turn wakeboarding, and after riding a bit, I did a faceplant. I don't really remember much, but when I didn't know what lake we were on, they took me to the ER. I suffered a concussion, had amnesia for a couple of hours, not fun...

Anyhow.. I replaced the fuel lines today, but I'm not optimistic it will make much difference. Old ones were original, but don't see any obvious problems.

I can try putting points back in -- but I'm not certain of the wiring... Wire from condensor/points goes to (-) on coil, and ballast resistor goes to (+) on the coil?? Is that right?

j.mccreight@hotmail.com
10-06-2013, 05:52 PM
So I took it out two weeks ago after replacing the distributor cap.
It was running terribly, until I figured out that after the compression test, I let my family assist with replacing the plug wires, and several of them weren't seated correctly. After I pushed them on good, it was back to how it was before (idling fine, still having trouble on accel)

I also checked for vacuum leak by spraying wd40 around the base of the carb, but didn't find anything..

We had my sister-in-law with us, so the family wasn't very patient with me messing the engine, they just wanted to play... Put on the barefoot boom and taught sis-in-law to wakeboard. Then I took a turn wakeboarding, and after riding a bit, I did a faceplant. I don't really remember much, but when I didn't know what lake we were on, they took me to the ER. I suffered a concussion, had amnesia for a couple of hours, not fun...

Anyhow.. I replaced the fuel lines today, but I'm not optimistic it will make much difference. Old ones were original, but don't see any obvious problems.

I can try putting points back in -- but I'm not certain of the wiring... Wire from condensor/points goes to (-) on coil, and ballast resistor goes to (+) on the coil?? Is that right?


yes

1redTA
10-06-2013, 07:10 PM
Check the spring that controls when the secondaries open. Mine was broke at it would fall on its face at wide open throttle and eventually gather speed

hairlesshacker
10-14-2013, 11:17 PM
Put in new fuel hoses.. That didn't help... So I tried pbgbottle's suggestion of putting the points back in... Again no luck, still same problem. (I should have known better, since it ran fine last year on the electronic ignition, but I figured it couldn't hurt to try it...)

I'm starting to get desperate.. My favorite time to ski here is when it's cold enough the lakes are pretty empty.
And I don't mind a slow horrible pull in the warm weather.. But in wetsuit weather, it's nice to be able to get up on slalom without getting my hair wet. (well, I'm bald, but you know what I mean...)

I guess I'll try changing the accelerator pump nozzle.. Or maybe pick up a rebuilt carb from national carburetors...

Alternatively, does anyone have a recommendation for a good mechanic who's familiar with the older boats in the Fort Worth area?

pbgbottle
10-14-2013, 11:39 PM
Sorry for getting you to mess with the points
Oh well. I would probably pull the carb apart
And check it ,
if it was rebuilt with a Holley carb renew kit it will have the newer style reusable
Blue gaskets. U can open it up carefully and not damage the gaskets
It is probably back firing because of excessive amount of fuel being dumped into the carb flooding it causing it to first hesitate and Then cough or backfire after ,

is it backfiring Out the mufflers or burping back up the carb. ?

thatsmrmastercraft
10-14-2013, 11:47 PM
I keep going back to your first post where you said it's been hard to start since you went through the carb. I would pick up a new accelerator pump diaphragm, spring and carb base gasket and replace the accelerator pump. Inspect spring location when disassembling.......I have found springs on the wrong side before.

If you are running way too rich, you could have a blown power valve. Have you checked this. If you do go inside the fuel bowls, be sure to check float levels.

hairlesshacker
10-15-2013, 12:41 AM
I did check the power valve about a month ago...
turned the two idle mixture screws in all the way (following holley's instructions for checking the power valve). Engine died as expected. I actually bought a replacement one, but didn't put it in since it passed this test..

I guess I'm not sure what the accelerator pump stream is supposed to look like, but when I pull the throttle, I see it squirt a stream of fuel in. A few weeks back I tried moving the pump cam from the 1st hole to the second, and tried adjusting the spring/screw, but I didn't seem to make any difference, so I set it back the way it was.

I actually still have the old pump diaphragm and spring from when I did the renew kit.. Will I be able to tell if there's something wrong with the current one? (would it be torn or something, or would a defect be something I wouldn't see?) And the spring goes in first, then the diaphragm, then the cover/arm? So the spring is between the bottom of the bowl and the diaphragm, is that right? (I haven't looked at this in a while, I don't recall how I put it together)

Another thing i'm not sure about is the base gasket. It's been a while since I put the carb on, but as I recall, I didn't have a new base gasket, or the right one wasn't with the renew kit, so I re-used the old one..
I don't really recall how this went, is there a gasket between the intake and the riser, and another one between the riser and the carb?