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AQ 131 still stumbles above 4000 rpm

R

robj

Regular Contributor
"Hello,

I have posted on th

"Hello,

I have posted on this problem earlier, and have tried everything. The engine runs great below 4000, but above it stumbles and surges. Have rebuilt the carb, went to Pertronix ignition, everything seems to be OK. It has the single barrel Solex downdraft carb. Are these things known for icing up? When I was running for a while at 3400 rpm, I stopped and checked the carb, it was quite cold and was wondering if these things have a history of icing problems? Just a WAG on my part as I try and figure this thing out.

Thanx and have a great day

Rob."
 
"Rob, out of curiosity, have y

"Rob, out of curiosity, have you tried with a different distributor or a different carb? Sometimes, when one runs out of ideas, that seems to be the only solution to find which component is giving you grief."
 
"Hello,

No I have not tried

"Hello,

No I have not tried a different distributor, don't have one. Have gone through the carb several times and it still does the same thing. Don't have an extra one of those laying around either.

Thanx for your suggestions and have a great day

Rob."
 
"Carb icing is possible under

"Carb icing is possible under the right circumstances. High humidity and low temps can contribute as can moisture in the fuel. It really is a long shot though. If you're using fuel with ethanol, have changed the fuel filter, and are sure the fuel is clean, then you have done about all you can on the fuel side. Make sure there aren't any other restrictions in the air intake that would increase the vacuum in the carburetor throat. In an inboard situation, and with the engine warmed up, the air in the doghouse would be a little warmer than outside so that would help avoid carb ice. I suppose it's possible with really high humidity and all the righ conditions but really a long shot. Have you noticed condensation or exterior ice at the base of the carb?

Have you checked timing to see that it advance slowly as RPM increases? The advance mechanism could be stuck or the springs may be missing or broken.

Just throwing in my 2 cents worth to try to help."
 
"Hello,

Thanx for the feedb

"Hello,

Thanx for the feedback. Hopefully there isn't any excessive play between the shaft and the distributor because that would be a pain to change. So on that point, I am unsure but will check. Regarding icing, it is a WAG on my part. Fortunately, we do not yet run ethanol here, but will do so in the near future, thanks to our provincial government. That stuff is trouble and the so-called environmental benefits are bogus. Save that debate for elsewhere. But when I touched the carb after running at 3400 rpm for awhile, it was definitely cold which made me wonder if icing could be my problem. It is wierd, runs great upto about 4000, and then trouble, starts to stumble. It will run for 5 to 10 seconds at 4800 and then drops down to 4200 and fluctuates between 4000 and 4400. I don't run it that high but would at least like to run it at around 4400 rpm, but can't. Normally I cruise at around 3400 rpm.

Thanx again for the suggestions. It may take a Weber to resolve this, but rather not spend the huge $$ if I do not have to.

Have a great day

Rob."
 
"Rob, did you try hotwiring th

"Rob, did you try hotwiring the + of the coil with the + of the battery, then run the boat under load at 4000 RPM? That would either discard or confirm a fault in the ignition switch or on the wiring from the ignition switch to the + of the coil."
 
"Sounds like my 5.0L. Ran grea

"Sounds like my 5.0L. Ran great upto 4200 rpm...throttle any higher and it would bog. Replaced fuel line from pump to carb (had a small kink)and filter. It now redlines at 5800 rpm...I know El, 4400 is recommended. I will see the prop doctor next week to fix that!"
 
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