18 replies to this topic

[Chelsea_Pete]

Hi all, and Merry Christmas

 

 

I'm trying to diagnose a fault on my hif44 carb, and could use a helping hand before giving it a complete overhaul.

 

Firstly, when accelerating hard, and especially when the engines cold, I get a cough , or miss, followed by a slight dip in power and sometimes a smell of petrol. No issues with stalling or starting, but recently i'll need to give it a good amount of juice or pull the coke out when pulling away in to overcome the sudden dip in power. Other than this it runs very smoothly which confuses me

 

Had a quick look in float chamber and there's no signs of dirt at a glance. Dashpot is topped up.

 

Got a Stage 1 kit with a cone-type air filter on it, perhaps its leaking or dirty, would that cause this fault? Or does it sound more like a blocked jet or float chamber in need of resetting? Timing even?

 

Secondly, there appears to be fuel leaking from the carb over the bulkhead, obviously a hazard which I need to tackle as a priority, but not sure how the two are related. Will replace gaskets and pipes and see if that solves the leak. Doesn't appear to be coming from the overflow as that's set to dump the petrol well away from the exhaust.

 

Help will be much appreciated, Im not well accustomed to carb diagnostics, but trying to learn haha

 

Thanks all, Pete

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[cal844]

What oil was used previously in the dashpot?
What work have you carried out in the vicinity of the carb?
Where is the fuel leak????

[dyshipfakta]

Sort the fuel leak you wil likely solve the issue. Don't drive it until it's fixed carb is above the hot exhaust manifold and near all the electrics.

[Dusky]

Don't accelerate hard with a cold engine, no carb can keep us with that. It LL wear your engine a lot too.
Probably the float gasket on the bottom that's leaking, a common fault

[cal844]

Don't accelerate hard with a cold engine, no carb can keep us with that. It LL wear your engine a lot too.
Probably the float gasket on the bottom that's leaking, a common fault

Our hif carbs(we have 5, either on cars or as spares) aren't fitted with gaskets on the float cap, they don't leak, not saying there isn't seals for this area just what I have....

I agree with you on the hard acceleration, although its hard not to when there is a fairly steep hill or 2 within 2 miles......

Edited by cal844, 23 December 2016 - 10:40 PM.

[panky]

My mildly uprated 1098 Minor does the same thing (except for the petrol smell) I just have to nurse it a little until it's warm and then it's fine. I do have that problem with a hill right outside my door though   It was fine with an AAU needle but after fitting a Midget exhaust manifold I went to an AAA, improvement all round except for the initial cold running.

[Dusky]

Don't accelerate hard with a cold engine, no carb can keep us with that. It LL wear your engine a lot too.
Probably the float gasket on the bottom that's leaking, a common fault

Our hif carbs(we have 5, either on cars or as spares) aren't fitted with gaskets on the float cap, they don't leak, not saying there isn't seals for this area just what I have....

I agree with you on the hard acceleration, although its hard not to when there is a fairly steep hill or 2 within 2 miles......

Can't imagine it wouldn't leak without a gasket or seal ring there.
I have a steep hill just when I come out the garage (must love the Flemish Arden's)
I go in low gears with little load and just accept the fact I'm a bit under the speed limit. Must say it comes of the choke quickly after I plumbed the heated manifold, but that's a different topic:)
Merry Christmas!

[Chelsea_Pete]

What oil was used previously in the dashpot?
What work have you carried out in the vicinity of the carb?
Where is the fuel leak????

Thanks chaps, Ill try and sort that leak and report back.

 

Cal,  I can't spot exactly where the leak is coming from, but there are deposits of fuel on the bulkhead directly below the carb. The dashpots only got 20w50 in it :/
Was tuned up with a new needle and a clean about 2 years back and hasn't really been touched since.

 

Dusky - actually there IS no gasket on that float chamber currently, ill make one up and see in that solves the issue. 

 

Annoyingly, after taking the chamber off to inspect this morning , the loss of power between gear changes and accelerating is now worse!

[cal844]

What oil was used previously in the dashpot?
What work have you carried out in the vicinity of the carb?
Where is the fuel leak????

Thanks chaps, Ill try and sort that leak and report back.
 
Cal,  I can't spot exactly where the leak is coming from, but there are deposits of fuel on the bulkhead directly below the carb. The dashpots only got 20w50 in it :/
Was tuned up with a new needle and a clean about 2 years back and hasn't really been touched since.
 
Dusky - actually there IS no gasket on that float chamber currently, ill make one up and see in that solves the issue. 
 
Annoyingly, after taking the chamber off to inspect this morning , the loss of power between gear changes and accelerating is now worse!

20/50(engine oil) is what's in my cars, they run great. What did you remove from the carb? Just the baseplate(for float chamber)?

[Chelsea_Pete]

 

 

What oil was used previously in the dashpot?
What work have you carried out in the vicinity of the carb?
Where is the fuel leak????

Thanks chaps, Ill try and sort that leak and report back.
 
Cal,  I can't spot exactly where the leak is coming from, but there are deposits of fuel on the bulkhead directly below the carb. The dashpots only got 20w50 in it :/
Was tuned up with a new needle and a clean about 2 years back and hasn't really been touched since.
 
Dusky - actually there IS no gasket on that float chamber currently, ill make one up and see in that solves the issue. 
 
Annoyingly, after taking the chamber off to inspect this morning , the loss of power between gear changes and accelerating is now worse!

20/50(engine oil) is what's in my cars, they run great. What did you remove from the carb? Just the baseplate(for float chamber)?

 

Yea I've heard varying reports as to whats best in there. 
My bad - wasn't the float chamber I removed, it was the dashpot/suction chamber on top (thats where there was no gasket). Havnt yet touched the baseplate

[Magneto]

I was wondering how you got the float chamber cover off in the car.......

 

It sounds lean when it's cold, my suggestion would be to put a lighter oil in the dashpot - as the stiff oil is keeping the needle down when it's cold, thus leaning the mixture....it's an easy thing to try and won't negatively affect anything else.

[Chelsea_Pete]

I was wondering how you got the float chamber cover off in the car.......

 

It sounds lean when it's cold, my suggestion would be to put a lighter oil in the dashpot - as the stiff oil is keeping the needle down when it's cold, thus leaning the mixture....it's an easy thing to try and won't negatively affect anything else.

Good advice, Ill get my hands on some 3 in 1.

 

Leak is definitely from the baseplate, ran my finger around it and soaked in petrol. Have taken it off and resealed with a [handmade] gasket. Time will tell if its worked 

[Magneto]

Doesn't the float bowl cover use an o-ring seal?

[carbon]

 

I was wondering how you got the float chamber cover off in the car.......

 

It sounds lean when it's cold, my suggestion would be to put a lighter oil in the dashpot - as the stiff oil is keeping the needle down when it's cold, thus leaning the mixture....it's an easy thing to try and won't negatively affect anything else.

Good advice, Ill get my hands on some 3 in 1.

 

Leak is definitely from the baseplate, ran my finger around it and soaked in petrol. Have taken it off and resealed with a [handmade] gasket. Time will tell if its worked 

 

If you think it's running lean then using a thinner oil won't help.

 

Keeping the piston down makes the mixture richer. For the same reason fitting a stronger dashpot spring also makes the mixture richer (the yellow spring being stronger then the standard HIF red spring).

[Magneto]

How do you figure that? The mixture gets richer when the pot moves up drawing the needle with it out of the jet. If something prevents this from happening - thick oil, too stiff a spring - then as the throttle plate opens allowing more air in the mixture gets weaker - thus you get a lean stumble.

 

Seems to me that's how it works anyway......

Edited by Magneto, 24 December 2016 - 10:58 PM.