mpt
Contributing Member
My boat is a 32' 1981 Bayliner Explorer. It has twin Volvo 140 4 cyl engines equipped with twin Solex side draft carburetors.
The recent symptoms are that when the port engine is warmed up, I can't get a smooth idle at 900rpm! It's not too rough of an idle, but when you chunk it in gear, the engine sounds rougher and drops down to 700-750 rpms. It only smooths out with more throttle(because of the shared intake manifold to all 4 cylinders). The starboard engine doesn't behave in this manner. When in gear it only drops around 50-100 rpms and purrs like a kitten.
A possible culprit could be the rear carb that feeds #3 and #4 cylinder.
One test I performed was that during idle, I pulled #4 plug wire and it didn't change idle or make engine run any worse!!
I also did the same with #3 plug wire and it changed slightly for worse.
When I pulled #2 it ran a lot rougher.
I suspect the front carburetor is compensating for the rear carburetor's performance. Oh the joy of sharing the same intake manifold!
Other trouble shooting I've done was:
1.) swap dist caps and rotor- same results! (starboard engine runs good with swap)
2.) replace port engine plug wires and plugs with brand new ones- same results!
3.) adjust idle speed and idle mixture screws- same results!
4.) pulled rear carb, split open, inspect (looked very clean), reassemble and re-install- same results!
5.) checked timing- looks good!
Years ago, I replaced the points and condensers with Pertronix on both engines, so I can't trace it any possible timing issues.
The old spark plugs I pulled, all looked the same as if they were burning normal. The electrodes had signs of wear, but their color was not brown or black, just whitish.
More trouble shooting I can do is:
1.) do another plug check on all 4 cylinders.
2.) double check timing
3.) compression check on all 4 cylinders
4.) swap rear carbs with starboard engine to see if I get the same rough idle problem. If this fixes the problem then I need to think about having the carb rebuilt or replaced!
I might have it narrowed down to a carb problem, what do you think?
The recent symptoms are that when the port engine is warmed up, I can't get a smooth idle at 900rpm! It's not too rough of an idle, but when you chunk it in gear, the engine sounds rougher and drops down to 700-750 rpms. It only smooths out with more throttle(because of the shared intake manifold to all 4 cylinders). The starboard engine doesn't behave in this manner. When in gear it only drops around 50-100 rpms and purrs like a kitten.
A possible culprit could be the rear carb that feeds #3 and #4 cylinder.
One test I performed was that during idle, I pulled #4 plug wire and it didn't change idle or make engine run any worse!!
I also did the same with #3 plug wire and it changed slightly for worse.
When I pulled #2 it ran a lot rougher.
I suspect the front carburetor is compensating for the rear carburetor's performance. Oh the joy of sharing the same intake manifold!
Other trouble shooting I've done was:
1.) swap dist caps and rotor- same results! (starboard engine runs good with swap)
2.) replace port engine plug wires and plugs with brand new ones- same results!
3.) adjust idle speed and idle mixture screws- same results!
4.) pulled rear carb, split open, inspect (looked very clean), reassemble and re-install- same results!
5.) checked timing- looks good!
Years ago, I replaced the points and condensers with Pertronix on both engines, so I can't trace it any possible timing issues.
The old spark plugs I pulled, all looked the same as if they were burning normal. The electrodes had signs of wear, but their color was not brown or black, just whitish.
More trouble shooting I can do is:
1.) do another plug check on all 4 cylinders.
2.) double check timing
3.) compression check on all 4 cylinders
4.) swap rear carbs with starboard engine to see if I get the same rough idle problem. If this fixes the problem then I need to think about having the carb rebuilt or replaced!
I might have it narrowed down to a carb problem, what do you think?