Club 80-90 Forums

Hi,

Has anyone successfully fixed a flat spot / hesitation? I’ve been unsuccessful in sorting mine out and its starting to become irritating when driving. There are times when its almost unnoticeable, others when requires a definitive change in throttle position to keep up speed. Some points that may help:

• Mostly happens in what I would call low rev range after changing gear. MUCH worse when cold too.
• Engine starts first time and ticks over lovely.
• Changed push rod.
• Change accelerator diaphragm
• Changed fuel filters.
• Cleaned out carbs.
• When the hesitation is there it feels like for a moment or two he’s firing on three rather than all cylinders – then when I put my foot down there’s a sudden power surge and away he goes.

All advice welcomed!

Tony

Have you checked the ht leads? Could try a known good ignition amp'.
David.

jrt wrote:Have you checked the ht leads? Could try a known good ignition amp'.
David.

Will do....currently reading through this at Kev's suggestion - http://forum.club8090.co.uk/viewtopic.p ... &start=225" onclick="window.open(this.href);return false;

Check your coil, instructions are in the wiki.

My coil was out of wack and was causing a flat spot/hesitation when i was driving.

New coil fixed it for me.

Cheers

Andy

Dhammadad wrote: Will do....currently reading through this at Kev's suggestion - http://forum.club8090.co.uk/viewtopic.p ... &start=225" onclick="window.open(this.href);return false;

A common cause of hesitation is the accelerator pump. You say you've changed the accelerator diaphragm, but it's possible you're still not getting enough extra fuel when you push the throttle. The cam on the end of the throttle spindle needs to be adjusted. There's a spec for the amount of fuel that should be squirted, but as a first step you could adjust it so that the cam is *just* touching the lever - this'll give you the maximum squirt, and if this was the cause of your flat spot then 'maximum squirt' should cure it. My experience with this adjustment starts a little earlier in that thread, here.

Undo the screw, push the cam to the left until it's just touching the curved end of the accelerator pump 'handle', then tighten the screw. Check the operation of the pump by removing the pancake and watching for a squirt of fuel when you operate the throttle.

CJH wrote:

Dhammadad wrote: Will do....currently reading through this at Kev's suggestion - http://forum.club8090.co.uk/viewtopic.p ... &start=225" onclick="window.open(this.href);return false;

A common cause of hesitation is the accelerator pump.....

Thanks,

Worryingly I have noticed that there isn't ANY fuel being squirted when i move the pump manually at all.

I guess that'd do it!!!

Dhammadad wrote: Worryingly I have noticed that there isn't ANY fuel being squirted when i move the pump manually at all.

I guess that'd do it!!!

It certainly will

So check that your new diaphragm has the right length rod, that it was assembled correctly (with the rubber mushroom, spring-steel disc/washer thingy, and spring, and maybe even check the strength of the spring in the new diaphragm - a good one will take approx 2kg to move the ball bearing against the spring.

Got that sunk feelin' now as this is one thing I did replace and made sure it was fitted properly.

Dhammadad wrote:Got that sunk feelin' now as this is one thing I did replace and made sure it was fitted properly.

Hmmm. Well if the pump is assembled correctly and in good order, but it's not pumping fuel, that can only be down to a few things. Is there fuel in the float bowl? Is the jet itself blocked or damaged?

CJH wrote:

Dhammadad wrote:Got that sunk feelin' now as this is one thing I did replace and made sure it was fitted properly.

Hmmm. Well if the pump is assembled correctly and in good order, but it's not pumping fuel, that can only be down to a few things. Is there fuel in the float bowl? Is the jet itself blocked or damaged?

Thanks, I'll double check - seems odd though that with a little more throttle he picks up fine. Thats what initially made me think electrics?

Dhammadad wrote: Thats what initially made me think electrics?

Well it could be that too

But if your accelerator pump isn't doing anything, you'll definitely have a (very) flat spot, most noticeable when you pull away from stationary. I had learned to pump the throttle myself, in anticipation of the flat spot, but with the accelerator pump adjusted properly it pulls away strongly all by itself.

CJH wrote:

Dhammadad wrote: Thats what initially made me think electrics?

Well it could be that too

But if your accelerator pump isn't doing anything, you'll definitely have a (very) flat spot, most noticeable when you pull away from stationary. I had learned to pump the throttle myself, in anticipation of the flat spot, but with the accelerator pump adjusted properly it pulls away strongly all by itself.

Not so much when I pull away - he's actually very smooth then. More when going from 2nd to 3rd - there's a definitive drop in power. If I keep my foot there....nothing changes, if I give him more throttle he seems to 'recover' and get a new wind - as it were.

That doesn't really sound like a problem with the accelerator pump in that case. So I guess there must be a simple explanation for why it didn't seem to be pumping when you checked. Can't really think what though, apart from an empty float bowl, but that doesn't seem likely if you've run the engine recently. Perhaps if the jet isn't pointing correctly you may not get a visible jet, but the fuel might still be getting in by hitting something else and dribbling down the walls of the venturi.....

CJH wrote:That doesn't really sound like a problem with the accelerator pump in that case. So I guess there must be a simple explanation for why it didn't seem to be pumping when you checked. Can't really think what though, apart from an empty float bowl, but that doesn't seem likely if you've run the engine recently. Perhaps if the jet isn't pointing correctly you may not get a visible jet, but the fuel might still be getting in by hitting something else and dribbling down the walls of the venturi.....

Thanks again, I'll have another look as soon as I can and report back!

Had the same with mine for a long time. The problem would come and go, never at idle or high revs but always after changing gears at low revs while the engine warmed up. Eventually solved it by cleaning and lightly oiling the spinning weights in the bottom of the distributor.