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JBB
08-29-2009, 05:43 PM
Posted a thread a couple weeks ago about my '88 prostar with 351 Indmar. The engine starts and idles great but starts shuttering/losing power around 1500 rpm wether in the lake or under the carport. I've done the following:
1. Rebuilt carb
2. Replaced filters
3. New fuel line
3. Checked all tank fittings
4. Checked fuel pump pressure
5. New points, cap, rotor, wires, plugs
6. Checked/lubed distributor weights/springs. Rotor shaft was seized up and i fixed that.
7. Baffles in muffler were broke and obstructing so i replaced with straits
All of this and still the same. I am going to verify the timing but know that this hasn't been screwed with since it last ran right. I feel like it is something associated with the distributer. Also, I noticed some oil residue coming from the valve covers at the low end (back). Obviously I need new gaskets but could this be causing a vacuum leak. Please help anyone!!

FrankSchwab
08-29-2009, 06:29 PM
I got no answer for you, but I'll add a comment to see if it brings in a few more readers.

Seriously, good luck. I hate those kinds of problems. It sounds electrical to me, as you're getting the same results under load or no load, based on RPM. The spark system really doesn't care much about load most of the time, but is heavily RPM dependent. However, this problem needs an experienced mechanic, and my best shade-tree mechanic days are long behind me.

Have you checked compression? It seems the only thing you haven't mentioned. Perhaps a bad coil? Does the stuttering happen on the lake at all throttle settings as you go through 1500 RPM (can you whack the throttle wide open and have it work better)? Any black smoke or heavy gas smell out the exhausts at this point (flooding)? Have you tried pouring a tiny bit of gas down the carburetor when this happens (starving)? Hook up a timing light and watch the timing as you throttle up - if it's erratic, that's a good hint.

Hopefully one of the engine masters on here will be by to help out; those questions are just to keep you busy until someone who knows what they're talking about shows up.

/frank

JimN
08-29-2009, 07:31 PM
Posted a thread a couple weeks ago about my '88 prostar with 351 Indmar. The engine starts and idles great but starts shuttering/losing power around 1500 rpm wether in the lake or under the carport. I've done the following:
1. Rebuilt carb
2. Replaced filters
3. New fuel line
3. Checked all tank fittings
4. Checked fuel pump pressure
5. New points, cap, rotor, wires, plugs
6. Checked/lubed distributor weights/springs. Rotor shaft was seized up and i fixed that.
7. Baffles in muffler were broke and obstructing so i replaced with straits
All of this and still the same. I am going to verify the timing but know that this hasn't been screwed with since it last ran right. I feel like it is something associated with the distributer. Also, I noticed some oil residue coming from the valve covers at the low end (back). Obviously I need new gaskets but could this be causing a vacuum leak. Please help anyone!!

If you changed the points, you HAVE TO check the timing. It's never the same after changing any ignition parts that may require adjustment. Look at the timing mark- if it jumps around, the bushing(s) have worn. Valve covers have nothing to do with vacuum.

You need only a few things for a motor to run properly. Compression, proper air/fuel mix and spark at the right time in relation to the valves and pistons.

Check the timing and set it at idle. Take it out on the water for any other performance related adjustments. None of them will be correct if you do them on the trailer. The motor must be under load and you can't provide that unless it's in the water. Did you check the compression? (needs to be done with the motor at normal operating temperature, all plugs removed)

If you can, do a vacuum test. That and the compression will indicate the general health of the motor.

JBB
08-29-2009, 09:27 PM
Ok. Sounds like i have three major things left to do. Check timing, compression, and vacuum. I sprayed some carb cleaner around intake while running but no reaction. Is there something more to testing vacuum. Also, JimN, I think I saw a thread you posted on how to test compression. I'll try to find that. Thanks.

JBB
08-29-2009, 09:42 PM
I had an extra coil and it did the same with it. Engine accelerates fine until it gets around 1500rpm and start shuttering and if I keep throttling it will just bog down. If i just shower down on the throttle is just wants to choke out. No black smoke or excess fuel odor

JimN
08-29-2009, 09:59 PM
Ok. Sounds like i have three major things left to do. Check timing, compression, and vacuum. I sprayed some carb cleaner around intake while running but no reaction. Is there something more to testing vacuum. Also, JimN, I think I saw a thread you posted on how to test compression. I'll try to find that. Thanks.

Vacuum gauge for testing that. Carb cleaner just shows where a leak is if it's around the intake manifold but there are other places it could be leaking. If getting it down to 650RPM for idle takes a lot of messing with the carb, a leak is a possibility. How clean is the flame arrestor? If it's clean and you have carb cleaner that makes the RPM increase, give it a shot of that at 1500 RPM when it lags to see if it wants to increase or decrease the RPM. If it increases, it's a lack of fuel and if it decreases, you may already be running rich.

JBB
08-29-2009, 10:46 PM
Where do i connect the gauge and what is the acceptable range?

JimN
08-30-2009, 11:05 AM
Where do i connect the gauge and what is the acceptable range?

I would try to find a service manual for this motor.

JBB
08-30-2009, 03:22 PM
Ok, I checked compression and I'm getting:
1-151
2-149.5
3-149.5
4-149.5
5-149
6-149
7-148
8-149.5
Checked vacuum and I'm getting 16-17 inches at idle and 20" at 1500rpm before it starts to shutter/bog. I also shot carb cleaner through the flame arrestor and the rpm decreased. Also when I pulled the new plugs they were fouled up.

JBB
08-30-2009, 03:25 PM
Forgot to mention that I have not checked timing yet. Waiting on a buddy to do it for me. I've got his timing light but haven't found any step-by-step instructions on here to help me do it.

JimN
08-30-2009, 03:41 PM
Forgot to mention that I have not checked timing yet. Waiting on a buddy to do it for me. I've got his timing light but haven't found any step-by-step instructions on here to help me do it.

Mark the groove on the balancer (behind the crank pulley) with chalk or something to make it more visible. Dust works in a pinch.

Connect the clip-on pickup to the #1 plug wire, connect the red clip to the battery + and black to battery -. Start the motor and squeeze the trigger on the light, looking at the timing mark in reference to the metal tab or other indicator on the block. If it's only a metal rod with a point, it should indicate degrees on the balancer. If it has no degree marks, the motor should have a metal tab with kind of a sawtooth edge and a mark for Top Dead Center (TDC) or degree marks. It may even has a O and a second groove in the tab, which would be the correct advance if the motor hasn't been altered.

If you look at the valve covers, you may see a sticker with model number, spark plug part number and gap, along with the correct timing advance. If you don't have that, set it to 6BTDC (Before TDC). Once you snug the distributor bolt, check it again to verify that it didn't move (you can do this while the motor is running). While it's running, increase the RPM and watch for the timing mark to move farther from TDC. If it doesn't move, te\he advance weights and springs need to be looked at, as well as the base plate.

JimN
08-30-2009, 03:44 PM
Ok, I checked compression and I'm getting:
1-151
2-149.5
3-149.5
4-149.5
5-149
6-149
7-148
8-149.5
Checked vacuum and I'm getting 16-17 inches at idle and 20" at 1500rpm before it starts to shutter/bog. I also shot carb cleaner through the flame arrestor and the rpm decreased. Also when I pulled the new plugs they were fouled up.

Some carb cleaner doesn't burn well. You can also use an old mustard bottle that has been cleaned to squirt some gas in through the flame arrestor. Make sure you have a fire extinguisher for that one, though.

Great compression numbers, BTW.

If you check the compression again, make sure to pay attention to the first spike of the needle. Higher is better.

Does your motor have a PCV valve that connects to the carb base? If it does, make sure it's good and not sticking.

TMCNo1
08-30-2009, 03:48 PM
IIRC, best done in the water in gear at 600 rpm idle speed.
6 degrees is third mark below the pointer.
Long red line on bottom pic.
51128

51129

JBB
08-30-2009, 04:08 PM
I took the pcv valve out and inspected it. The valve was free and rattled. Sucked on it and it opened. Blew on it an it closed. The hose from the pcv valve to the bottom of carb is where I connected the vacuum guage. I'll go try the timing light. These pictures will help.

FrankSchwab
08-30-2009, 04:34 PM
You said that the new plugs were fouled when you pulled them - was it gas or oil fouling?

JBB
08-30-2009, 06:42 PM
Timing is set dead on 10 btdc. The rotor shaft that connects to the weights was seized up but i cleaned and oiled it. The springs appeared to be ok. However, i didn't remove the weights or springs but they appeared to move freely. Is it time to focus on the distributor itself?

JBB
08-30-2009, 06:43 PM
Plugs were just coated with black carbon. They were not wet with fuel.

TMCNo1
08-30-2009, 09:39 PM
Timing is set dead on 10 btdc. The rotor shaft that connects to the weights was seized up but i cleaned and oiled it. The springs appeared to be ok. However, i didn't remove the weights or springs but they appeared to move freely. Is it time to focus on the distributor itself?

Appearing to be OK and appearing to move freely and actually doing so are two different things.
If your going to approach this half azzed, why bother asking and allowing us to waste our time.:twocents:

JimN
08-30-2009, 09:45 PM
Timing is set dead on 10 btdc. The rotor shaft that connects to the weights was seized up but i cleaned and oiled it. The springs appeared to be ok. However, i didn't remove the weights or springs but they appeared to move freely. Is it time to focus on the distributor itself?

Put the timing light and watch for the advance to increase as the RPM increases. This, you can do in neutral. As long as it increases smoothly, you should be OK but if you see the total advance shoot past 40BTDC and you're only at 2500 RPM, the springs are probably shot. OTOH, if you go close to WOT and you only see 20 of total advance, it means the weights, bushing and springs need work.

JBB
08-30-2009, 09:49 PM
Let me re-phrase, the springs looked in good shape and expanded/contracted as you would think a normally functioning spring would do. The weights were not cracked, looked to be in good shape, pivoted freely and i could work them (along with spring) with my finger with ease. TMCNo1, i AM half "azzed" right now because half of my azz has gone into fixing my boat for that last three weeks. I am quite alright if you don't waste your time anymore!

JBB
08-30-2009, 09:54 PM
Thanks JimN. I did not do tthis earlier (4 year old running around). I will do this and see what's happening. I know there are certain parts on this boat that need to be marinized. I'm assuming that the Distributor is one of them since it creates spark. Just wondering since a distributor at AutoZone is about $70.

TRBenj
08-31-2009, 04:33 PM
I agree that you need to set your timing and verify that its advancing properly.

Did you set your dwell when you installed the new points?

JimN
08-31-2009, 04:41 PM
Thanks JimN. I did not do tthis earlier (4 year old running around). I will do this and see what's happening. I know there are certain parts on this boat that need to be marinized. I'm assuming that the Distributor is one of them since it creates spark. Just wondering since a distributor at AutoZone is about $70.

Have the little one run for parts on their tricycle and coaster wagon. Just make sure the store knows they're authorized to use your credit card. :D

Marine distributors have spark suppression and cars don't need that but if you do replace the whole thing, get an HEI unit with electronic ignition. Far less to mess with and more reliable. I don't really have a problem with points at face value but they need to be adjusted, the wedge that rides on the cam wears 9changing the setting) and the condenser can go bad without any warning.

helton333
08-31-2009, 04:42 PM
Jim, sent you a pm - check it - sounds just like my 1989 ps issues - COIL!!!

JBB
08-31-2009, 08:19 PM
Ok, here is what it is doing. Timing advances smoothly only up to about 16deg with rpm at approx. 1500 (that is as high as it will go and run smooth). Once it is throttled past 1500 the timing starts jumping back and forth from approx. 0 to 40. JimN, from what you described it looks like it may be the springs. It may be worth just replacing springs, weights, and bushing. Can i get these from skidim? Is the bushing pretty easy to change?

JBB
08-31-2009, 08:23 PM
One other tidbit. I pulled the dipstick yesterday and it had a strong smell of gas. It was over the full mark which also indicated gas was in it. I guess this is a result of the jacked up timing?

JimN
08-31-2009, 08:37 PM
One other tidbit. I pulled the dipstick yesterday and it had a strong smell of gas. It was over the full mark which also indicated gas was in it. I guess this is a result of the jacked up timing?

At this point, since we know the oil smells like gas, I would change that and the filter and see what you can do about setting it to run leaner before anything else. The timing won't make it run that rich.

TCrate
08-31-2009, 10:26 PM
JBB if you have a lot of gas in that oil that is a sign of a bad/leaking fuel pump. That is dangerous and could be your problem as well. Is there a tube running from the pump to the carb and is there gas coming out of it into the carb. If so, this would explain the black plugs (RICH MIXTURE). Did you say you checked fuel pressure. It should be between 4-6 psi. Just a though. Tcrate

JBB
08-31-2009, 10:53 PM
I have not noticed any fuel coming from the overflow line (with all the work i've been doing on this thing i would have noticed it). The pump is consistenly showing 6psi. I'm perplexed. This thing cranks at the touch of the key, idles smooth and is fine up to 1500 rpm and then just starts crapping out. Is there something other than needing a carb adjustment that would make it run rich. The last few hours this thing has been running is has been at idle or low rpm. Will that foul plugs/let excess fuel get into oil. Leading up to this problem the boat ran great. It sat up for a while and some moisture got into enigine area. Had the points changed to get it cranked, took it to the lake and this problem occurred.

JBB
08-31-2009, 11:03 PM
I'm wondering if the fuel in the oil is a product of the fooling around with the carb (without engine running) that may have taken place trying to figure this problem out. Dispersed fuel by the carburetor that didn't get burnt.

JBB
08-31-2009, 11:09 PM
I can say with certainty that at the rpm's this thing is running ok at (idle, and low rpm) there not gas dripping from venturi's. It does not appear that there is fuel flowing in that isn't getting burnt (while running anyway). I checked that yesterday.

JimN
08-31-2009, 11:36 PM
I have not noticed any fuel coming from the overflow line (with all the work i've been doing on this thing i would have noticed it). The pump is consistenly showing 6psi. I'm perplexed. This thing cranks at the touch of the key, idles smooth and is fine up to 1500 rpm and then just starts crapping out. Is there something other than needing a carb adjustment that would make it run rich. The last few hours this thing has been running is has been at idle or low rpm. Will that foul plugs/let excess fuel get into oil. Leading up to this problem the boat ran great. It sat up for a while and some moisture got into enigine area. Had the points changed to get it cranked, took it to the lake and this problem occurred.

When the points were changed, what adjustments were done? The gap and dwell absolutely need to be correct.

JBB
08-31-2009, 11:52 PM
I will check with the mechanic. May have not been done. May need to figure out how to do that myself too.

JBB
09-01-2009, 09:10 PM
Changed the oil/filter/plugs and am waiting on a new set of springs and electronic conversion kit (decided to go ahead since i was changing every other dang thing out). Got to looking at the springs and weights and there is lot of loose play on one of the springs and weight (the springs looks a little bigger and it looks stretched out). Should there be this loose play? The other is held tight byt the spring.

2010Prostar197
09-01-2009, 10:27 PM
Definitely not an expert here but I had an 89 Supra with the 351 Ford using I believe the 4160 Holley carb.

It had the same symptoms as you and drove me nuts. It turned out to be the small (1 inch diameter) screw in valve that goes on the plate that is in between the fuel bowel and the main carb body. The valve was bad dumping gas in instead of metering it through the fuel metering jets. The way I understood it was the idle circuit works up to a certain vacuum and then this valve opens to open fuel to the main metering jets above 1200 to 1500 rpm. Maybe JimN can verify or correct me on this...

Just a thought...

I know things like this can drive a person nuts!!!

JBB
09-03-2009, 11:54 PM
Well I replaced the springs to see if that would do the trick and now it won't crank. Getting spark and fuel but all it will do is turn over. After every 5 or so revs fuel will "poof" out of the venturis. A couple of times it sounded like the engine burped. Makes me think that it's the timing. Nothing has changed since i cranked it last (yesterday). Does it sound like the bushing, gear, etc. is going bad in the distributor finally causing it not to fire and this has been the problem the whole time. Looks like no boating activities this weeked.

JimN
09-04-2009, 11:42 AM
Well I replaced the springs to see if that would do the trick and now it won't crank. Getting spark and fuel but all it will do is turn over. After every 5 or so revs fuel will "poof" out of the venturis. A couple of times it sounded like the engine burped. Makes me think that it's the timing. Nothing has changed since i cranked it last (yesterday). Does it sound like the bushing, gear, etc. is going bad in the distributor finally causing it not to fire and this has been the problem the whole time. Looks like no boating activities this weeked.

Remove the wire to the tach and see if it runs. While you're doing this, make sure the wire to the coil isn't touching the base of the distributor.

JBB
09-04-2009, 02:13 PM
Did that and same thing............"poof"! I think it is vapors out of the intake....not fuel out of the carburetor. Shined a timing light on it while it turned over and it is not off.

JBB
09-06-2009, 11:46 AM
I guess the next step is to pull the distributor and see what kind of shape it is in. At this point i may just order a new one with EI. If any of the senders went bad (water/oil), would it cause the engine not to start? Just a thought. Just confused as to why it won't start now.

JimN
09-06-2009, 12:35 PM
I guess the next step is to pull the distributor and see what kind of shape it is in. At this point i may just order a new one with EI. If any of the senders went bad (water/oil), would it cause the engine not to start? Just a thought. Just confused as to why it won't start now.

You don't have an ECM to receive info from a sender and kill the motor but as I mentioned, if you remove the tach wire (it's gray), it may start. If it does, it means the tach wire or the tach itself has a short. Grounding the tach wire will prevent spark. Make sure the terminals on any wires connected to the distributor are in good shape and not touching anything that's grounded.

JLeuck64
09-07-2009, 12:44 AM
Well I replaced the springs to see if that would do the trick and now it won't crank. Getting spark and fuel but all it will do is turn over. After every 5 or so revs fuel will "poof" out of the venturis. A couple of times it sounded like the engine burped. Makes me think that it's the timing. Nothing has changed since i cranked it last (yesterday). Does it sound like the bushing, gear, etc. is going bad in the distributor finally causing it not to fire and this has been the problem the whole time. Looks like no boating activities this weeked.

Did you set the dwell (or the point gap correctly) after doing this? I prefer to use a dwell meter when working around points. Beg, borrow or steal one and have somebody show you how to use it, it will make your life a LOT easier.

Beyond this, I will add one thing. I bought a set of points one time that must have been for a four cylinder engine. The spring was way too soft and the points would start to bounce around 1500 rpm. Might want to check your new points against your old points for this. It took me days to discover this and boy was I PI$$ED off at my parts guy when I finally figured it out...:mad:

Don't give up, if you are not frustrated you aren't learning!