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Old 09-14-2013, 01:19 AM
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hairlesshacker hairlesshacker is offline
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Boat: 1990 TriStar 190
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1990 Tristar hesitation/backfire

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..
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  #2  
Old 09-19-2013, 12:43 AM
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hairlesshacker hairlesshacker is offline
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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..)
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  #3  
Old 09-19-2013, 01:06 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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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
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  #4  
Old 09-19-2013, 02:18 AM
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Quote:
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...


Quote:
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
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Old 09-19-2013, 02:33 AM
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hairlesshacker hairlesshacker is offline
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Boat: 1990 TriStar 190
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Well, maybe I'm making a bad assumption, I thought the two springs should look identical...
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/pn...1001/overview/

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  #6  
Old 09-19-2013, 11:09 AM
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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!
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Old 09-19-2013, 11:17 AM
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ccelia ccelia is offline
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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).
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Old 09-19-2013, 11:18 AM
hairlesshacker's Avatar
hairlesshacker hairlesshacker is offline
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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.
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Old 09-19-2013, 11:21 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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Quote:
Originally Posted by drschemel View Post
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'
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Old 09-19-2013, 11:24 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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Quote:
Originally Posted by hairlesshacker View Post
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.
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