1989 Carb engine high revs?

RobMorris · Post by **RobMorris** » Wed Oct 14, 2015 1:10 pm

Hey guys

So my car was off the road a few years.

I have given it a service and battery charge but the engine idles really high? Like 1800 revs.

It also smokes quit a bit?

It starts straight away and goes up the road OK but the revs wont come down even when warm?

What should I try first?

Cheers!

Post by **RattyMcClelland** » Wed Oct 14, 2015 2:14 pm

The carbs need to come off and have a real deep clean. They are very sensitive to dirt and carbon build-up block venturi tubes that flow fuel. The carbs more than likely will need balancing with a good tune.
A job for a old skool mechanic.

Post by **Vtecmec** » Wed Oct 14, 2015 2:34 pm

Check everything moves freely too, including the throttle cable, which could be sticking.

RobMorris · Post by **RobMorris** » Wed Oct 14, 2015 2:48 pm

I did do a 'engine degreaser' and power wash when i first got it.

If I remember rightly it did not rev so highly before? Maybe stayed at about 1200 revs and never went down even when warm?

prelude91 · Post by **prelude91** » Wed Oct 14, 2015 6:10 pm

Give the carb inlet a good squirt of Redex, or similar modern equivalent. May unblock any jets gummed up. Quicker fix than starting by stripping the carbs straight off

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Wed Oct 14, 2015 10:53 pm

Sounds like an auto-choke sticking, or just plain not working, possibly with a base idle that is set generally slightly high...

(I assume they do have an auto choke, right? Of the bi-metallic electrically heated strip variety? Yes?)

If you start it from cold, don't drive it but just leave it idling to warm up, do the revs slowly creep up till they reach the 1800ish you mentioned?
If you then blip the throttle, do the revs stay that high, or do they drop back quite a bit?
If they don't drop back, the auto choke is staying closed (not opening).
If they do drop back a bit, it might not be fully opening, or it is properly opening but the base idle/mixture is just set very high.
The exhaust colour and smell is a bit of a clue here - if it's sooty and/or smells fuelly, then it's probably a sticking choke/mixture setting problem. If it's clean, then it's probably base idle.

I don't know what the carb position is like on this engine. Checking the choke flap operation is normally easy, provided you can take the inlet filter cover off and see into the top of the carb. If you can't, then it's much more awkward.

(If they're not auto-choke, then ignore pretty much all of the above...)

YouTube · Post by **Sailor** » Thu Oct 15, 2015 12:30 am

What carbs are they?

If the revs won't come back down again, you could start by checking that the butterflies aren't sticking.

RobMorris · Post by **RobMorris** » Mon Oct 19, 2015 12:12 pm

OK so here is the latest.

She was running low on fuel (3 years old fuel I assume) So I gave her a drink of 97 (5/lires)

From cold she revved up to 1800revs and after about 30 seconds dropped to around 1600revs before going up to 2000revs until around 10 minutes.

She was quite smokey and had a very strong smell of fuel.

As the water temp rose, the revs started to drop and settled once full warm at 1400 revs (12 minute mark)

Once warm I turned the Idle Adjust Screw so now when warm at least she ticks over nicely at around 800 revs!

So when I play with it next from cold - I need to adjust the fast idle screw I believe. If when on choke I can bring that down to 1600 revs I will be very happy.

YouTube · Post by **Sailor** » Mon Oct 19, 2015 3:44 pm

Yes, but you shouldn't have to do that every time.
It does sound like a choke problem.

Post by **RattyMcClelland** » Mon Oct 19, 2015 3:53 pm

Their Kehin twin motorbike carbs. Can't remember which exactly.

One day I'll have a 4ws ex with sidedraft webbers on it. One day.