A-65 stumbles

[Bob Greenwall]

My A-65 stumbles on opening the throttle, which it never used to do. If I nurse it through this rough spot it makes power fine. Any ideas?

[Pearson]

Re: A-65 stumbles

Bob,

Always look for the simplest solution first!

If you have the Stromberg NA-S3A1 or NA-S3B there is a common stumble at around a thousand rpm. But, if it is more than just a slight stumble there is something wrong. I would check for; clogged air filter, bad/contaminated gas, idle mixture needing adjusting, float level needing adjusting. If none of that takes care of it, you might have some debris in the idle air bleed.

Does any black smoke come out the exhaust when you try to advance the throttle? If so, you might try turning the idle mixture screw in a 1/4 turn. I usually turn mine in a little in the spring and back out a little when winter arrives.

[Vasey fan]

Re: A-65 stumbles

I'm assuming the engine is warmed up sufficiently. The little Continentals stumble pretty good if they're not warm & happy.

I'd look for an intake leak first.

[Howard Wilson]

Re: A-65 stumbles

Gunk in the Gascolator, or an air leak.

[M Towsley]

Re: A-65 stumbles

Bob,

Though this probably isn't the problem, check to make sure your primer is seated and locked. I left my primer out oh so little after the first start earlier this year and it ran terribly. It is an easy check, so make sure. I had a friend who had the pin end of the primer break off, causing similar problems. But all the other ideas are good to check. I found an intake leak by removing the carb and using a shop vac hose hooked to the exhaust portion of the vac. Make sure the vac, filters and hose are cleaned prior to doing this. Temporarily wire the end of the hose up into the intake spider. Turn it on and spray the intake points all along each tube, etc. with soapy water. It will spit bubbles, making it easy to see. Check your mixture screw first, though. That is the easiest.

[Bob Greenwall]

Re: A-65 stumbles

Thanks for the help, gents!

[alwaysoar]

Re: A-65 stumbles

These carbs have no accelerator pump. Also, the warmer weather has caused a change in mixture. If it did not stumble before, but does now, adjust the mixture.

[AndyDuke]

Re: A-65 stumbles

Also check that there are no leaks in the intake manifold. The common problem is that the jubilee clips that hold the intake rubbers vibrate loose causing leaning. When you accelerate you get a rough patch when the carb switches from the idle jet to the main jet.

[Len Petterson]

Re: A-65 stumbles

1 check so the fuel cock so it opens fully, check travel in the linkage etc.
2 check your fuel hoses for internal swelleing, Swelling internaly is redusing the fuel flow and will starve the engine of fuel for acceleration and high RPM.
And offcoarse check and clean the carb.
Mine would not accept trottle at all, died at 1200 rpm, less when 5/16 in 2 places in the hoses.
One time the valve would not open properly,it was sticky needed fuel lube.

Len

[astjp2]

Re: A-65 stumbles

I solved my proble by just having the carb heat out,,,,,when i acclerated on a go around, it would be throttle first and then carb heat, the richer mixture took care of the stumble. My permenant fix was to go with the Marvel Dribbler...... Tim