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Grrrrr - bloody car
davidimurray - 11/3/14 at 09:04 PM

Finally got my reg just before Xmas. Been out for a few drives and decided to take the car to work for the first time. Went great' just ticked over 300 miles and everyone loved the car and even a few test rides. Drove home and noticed a few pops and bangs at light throttle. Got home and noticed lambda had gone from 13 at idle to 14.4. Car was misfiring at low throttle but OK at wider openings. Whipped the pilots out of the bike carbs and cleaned them. Took out for a test drive and no better and still lean. So annoyed was really looking forward to taking her to work again tomo

AdrianH - 11/3/14 at 09:09 PM

Slight leak perhaps on inlet side or would it be the exhaust side never sure?

I believe you can get pops and bangs if on exhaust side on over run.

Can you test around the inlet manifold with a can of wd40 see if revs improve when going around the gasket area, or just check all is tight.

Adrian

Edit to add to thoughts, if leek on exhaust side it will lean off the lambda and add more fuel so that un-burnt fuel goes into the exhaust to cause the pops and bangs!

only guesswork.

[Edited on 11-3-14 by AdrianH]

davidimurray - 11/3/14 at 09:14 PM

quote:
Originally posted by AdrianH
Slight leak perhaps on inlet side or would it be the exhaust side never sure?

I believe you can get pops and bangs if on exhaust side on over run.

Can you test around the inlet manifold with a can of wd40 see if revs improve when going around the gasket area, or just check all is tight.

Adrian


Have tried around the carb rubbers and balance hoses with no change. I think its a proper misfire as it sounds like it is popping under the bonnet and also started hesitating. Wondering whether I could have a dead spark plug.

adithorp - 11/3/14 at 09:16 PM

Sounds like you've got an air leak. Prob' a vac pipe off, inlet gasket loose etc.

Spray a bit of carb cleaner around and if it goes near the leak you'll hear the engine note change. Alternative (and more accurate) is take the burner nozzle off a blow lamp and replace with a length of hose on and then feed the gas around the inlet side. Revs will raise when you find the leak. Only do in a well ventilated area though.

mccsp - 11/3/14 at 09:45 PM

Have you re-spaced the carbs? Could be the ballancing between the carbs. I have to reballance my throttle bodies periodically.

davidimurray - 11/3/14 at 10:03 PM

quote:
Originally posted by mccsp
Have you re-spaced the carbs? Could be the ballancing between the carbs. I have to reballance my throttle bodies periodically.


Carbs are respaced so will check the balance again tomo.

davidimurray - 12/3/14 at 06:48 PM

Update time.

Checked the balance and it was out. Rebalanced the carbs and it is a hell of a lot better, but still has a small misfire.sprayed all around the manifold and no change in engine note. Lambda is still showing a bit leaner than it was.

jacko - 12/3/14 at 07:01 PM

Exhaust look for small cracks near the plate that bolts to the head not me but some one i know had this happen on there car
They have a MK manifold fitted
Jacko

mccsp - 12/3/14 at 07:48 PM

Have you had the plugs out and cleaned them since setting the, could be fouled? Might be worth then rechecking ballance again.

davidimurray - 12/3/14 at 08:29 PM

Put a new set of plugs in and rechecked balancing which is spot on. Have also soaked around the manifolds and carbs with wd with no change in revs.

At idle the miss is like a little burble, at 2000rpm it is barely there, above 3000 it is like a machine gun!

Wondering if I should whip exhaust and inlet off and re seal? Any reccomendations for exhaust/inlet sealant?

I've whipped the main and pilots out and popped them in carb cleaner to soak but I doubt they are the cause.

Gave also checked crank sensor is secure and not moving.

mccsp - 13/3/14 at 12:12 AM

Is yur crank sensor wiring a twisted pair? If not could be getting noise issues, not sure why it would have changed.