Misfire under load
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=967
Printed Date: November-22-2024 at 8:03pm
Topic: Misfire under load
Posted By: Guests
Subject: Misfire under load
Date Posted: November-01-2004 at 8:34pm
I have a 87 Martinique, new to me. It misfires at the carburetor when the engine loads up during a hard acceleration or turn. The Engine maxes out at 3200 RPM. The family has another martinique that runs like a banshee all the way to 4400. The other one has much better hole shot, and a 1.23:1 reduction gearbox. Mine is 1:1.
I just had the carburetor rebuilt. I looked at the timing advance, and the two springs that retract the centrifugal weights are not identical.
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Replies:
Posted By: workky
Date Posted: November-02-2004 at 12:03am
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Have u checked the timing?
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Posted By: Britler
Date Posted: November-02-2004 at 5:38pm
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Just because the springs are not identical does not mean thats incorrect. Sometimes a combo needs to be used to be very specific. In my mind this is pretty far fetched for me to say but your timing would have to be quite a bit off to cause backfire through the carb. Look at it this way. Your timing would have to be so advanced that combustion leaking through your intake valve would ignight what is left in your carb and intake runners to cause that pop through the carb. Either that or you have the improper firing order which I have done multiple times! GO thorugh your timing and check for intake leaks. Your problem sounds like an intake leak to me. Whats probably happening is you are getting a lean hit so to speak and thats whats causing the pop. Fire up the engine and spry some carb cleaner around the whole intake system to see if you can find one. Good luck
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Posted By: 79nautique
Date Posted: November-03-2004 at 12:37pm
The factory springs and not the same so what you are seeing is correct. Since your RPM is so low I would say your issue is strictly a timing issue only. If you didn't replace the power valve during the carb rebuild you should do it now.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: captan1
Date Posted: November-19-2004 at 2:23pm
What about cross plug wire arc, its possible the wires are moving around during hard starts and cornering, I've never had that happen but I've heard of it. Electricity arcs across two plug wires firing the wrong cylinder at the wrong time,, when a intake valve is open. Make sure you use the plug wire separators to keep them from actually touching, and what ever you do don't tie strap them together.
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http://www.correctcraftfan.com/diaries/details.asp?ID=452&sort=&pagenum=1&yrstart=1978&yrend=1978 - 1978 Ski Nautique
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Posted By: Guests
Date Posted: January-03-2005 at 12:34pm
My name is de raaff from the netherlands Europe. I've searched for a long time before I solved my back-fire problem on a '94 ski-nautique.
The problems was a bad connection in a connector. The engine was running OK on all rpm's except sometimes on accelating from stationary. Sometimes he didn't backfire at all sometimes he did.
When i wired directly from the main connection to the power of the igntion unit it was all over that's the way I found the problem. Maybe it ca be the same situation by U.
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Posted By: 97sport
Date Posted: January-03-2005 at 2:15pm
all are good post. most of the time you get a back fire thru the carb is because of a lean fuel problem i.e accl pump, intake gaskets, low fuel settings in bowls, anything that won't supply the clys. with enough fuel.
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life is short live it!!!
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Posted By: Bradley950
Date Posted: March-09-2005 at 1:16am
I have cured this problem in the past by advancing the timing. Put a timing light on and turn your dist. clockwise to advance.
-Brad-
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Brad Miller
bradley950@yahoo.com
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Posted By: nates78ski
Date Posted: March-12-2005 at 3:53pm
Three thing will cause a backfire on acceleration. First is lean fuel, second incorrect timing and third weak spark. The old rule is if it backfires out the carb its lean, out the exhaust its rich.A weak coil or weak spark caused by an ignition problem will back fire out the carb which may lead you to think lack of fuel is the problem.
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Nathan
http://correctcraftfan.com/diaries/details.asp?ID=1463&sort=&pagenum=3&yrstart=1978&yrend=1978" rel="nofollow - My '78 Ski Nautique
<a href="http://photobucket.com/Nates78ski" rel="nofoll
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Posted By: Guests
Date Posted: March-12-2005 at 11:20pm
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you should check you exhaust manifold water could be leaking into the exhaust port of the motor causing preignition. which will come out of the carb and seem like a bad miss. hope this helps with your problem.
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Posted By: Guests
Date Posted: June-19-2005 at 2:52am
Hi Guys. Regarding the last post, how do you check to see if water is leaking back from the exhaust? Thanks,
Matt
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Posted By: axlr8or
Date Posted: June-19-2005 at 9:30pm
As many other guys have already stated, I'd be checking a few electrical things first (cuz its cheap). run it at night to check for spark plug/spark plug wire arcs. replace the distributor cap/rotor. get a new condensor. Possibly new points if that new of a motor uses points. All those things are cheap, and take a lot of age off of your motor when replaced. As said before, get a timing light and make sure mark lines up. Idle your motor for a while, when its good and warm listen for lifter noise (which may be caused by several things). Another cheap check is a vacuum gauge. They kick butt, they come with a visual diagram on how to diagnose valve train and carbuerator related problems.
If you had the carb rebuilt to solve this problem, and the problem still exists as it did before, and all the electrical/vacuum checks stated above check out, you most likely have a valve train related problem. Man, lets not forget it could even be an elevation problem at the fathest reaches (where do you live :D) Its always next to impossible to do a dead on dignosis of a problem without being there.
Good luck.
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