Poor running Carb

[stanleyboy]

Hi

1600cc on 68 with a standard single port engine with single carb.

have an issue where the engine struggles at about 1500/2000rpm then seams to clear and engine runs smoothly, it also starts every time and ticks over nicely.

Have tried carb cleaner whilst engine running but made no difference. I think there is only a single jet on right hand side of carb (looking into engine bay) As I have never remove anything from the carb, would this be the jet I would take off to see if any blockage?

Prob not enough info for a definitive answer but hopefully someone can help before I start mucking about.

regards

Andy

 

[jonboylaw]

Are you by any chance using a 009 dizzy ? Could will be an ignition problem rather than a carb fault.


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[stanleyboy]

I know I have a dizzy and points set up but have to admit I don't know how to identify if it's 009 dizzy
I have in the past year renewed the points, HT cables, dizzy cap and HT Coil.

 

[jonboylaw]

Does the dizzy have a vacuum canister on the side with a pipe going up to the carb ? If so then it is an SVDA. If not is could be a 009.
Have you always had this problem? If so and have a 009, it could well be the flat spot.


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[stanleyboy]

I must have a 009 dizzy as I do not have any tubes going to the carb.

 

[stanleyboy]

Well I could have put money on the fact that my dizzy did not have a vacuum or tube going to the carb.
So I now looked again and I have both a vacuum and tube to carb lol!

Took. Out the jet and blasted it with carb cleaner and took van out for a run. Runs a bit better but still has a hesitation between 1000/2000 rpm but not as bad as before.

 

[71Westy]

I'd check the timing and the points gap first before looking at the carb. Plus the usual check for air getting into inlet manifold somehow (squirt your carb cleaner at the various joints while the engine is running - you'll soon notice if there is a leak).

Then I'd check the carb set-up. It's worth checking the idle mixture (have a look at Rob n Dave's aircooled pages which have a good description). Another thing to check is the accelerator pump - make sure it's squirting on quick application of the throttle (just whip off the air cleaner, pull on the throttle arm whilst looking down the carb - you'll see it). If all that is ok you might have blocked jet or the wrong jets. Which means a carb strip, which isn't too bad.

 

[stanleyboy]

Thanks for advice. Engine runs really well before it hesitates and accelerates really well and smoothly after.
Will try out looking. Down into carb but will prob need a mirror or a smaller head this where an engine hatch would be good. The points were new about 1k ago but will have a check tomorrow.
Andy

 

[jonboylaw]

It could as said above be a faulty accelerator pump but this should show when strongly accelerating at all engine speeds. You could try accelerating the engine very gently through the flat spot to see if it still bogs down (probably not pump related). Do this whilst driving so there is load on the engine. Or get the engine through the flat spot and booting it to see if it pulls ok. That will tell you if the accelerator pump is ok.
Inspect the vac tube from carb for splits and also make sure the base plate in the dizzy is free to move and the advance springs are fine.




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