10 replies to this topic

[chlblnz]

I have a 1981 998 with electric dissi (Lumenition), HS4 carb.

The problem I have is the engine dies when I apply the throttle unless the choke is completely out. I initially thought it was either the timing or carb. Have set the timing as close as its going to get and rebuilt the carb, jet and needle look fine. Using AAC needle at the mo. Also have an ADE which when installed, problem works in exactly the same way. The float looks in good condition. Fuel pump is filling fuel filter up nicely.
Plugs are always black. Put this down to choke always being out.

Any ideas?

[n00b]

sounds like it could be running a wee bit on the leaner side. (when choke is not engaged) which is causing the engine to run smoother when more fuel is applied throught the carb.

You could try set the catb a little richer - taking into acount an ADE needle is richer by nature.

if not set it back to its original setting (use 1/4 turns)

if i remeber rightly the mixture adjustment is on the under side of the carb, changing mixtures according to directions is something you will have to look into.

ERic

[chlblnz]

sounds like it could be running a wee bit on the leaner side. (when choke is not engaged) which is causing the engine to run smoother when more fuel is applied throught the carb.

You could try set the catb a little richer - taking into acount an ADE needle is richer by nature.

if not set it back to its original setting (use 1/4 turns)

if i remeber rightly the mixture adjustment is on the under side of the carb, changing mixtures according to directions is something you will have to look into.

ERic

Hi

Thanks for the reply.

The choke has to be right out bringing the jet almost out of the carb itself. Even if i turned the fuel adjustment right down (when the choke is not engaged) it wouldn't be far enough.
I read in the Haynes about carb setup, and to test if its too rich/lean, I should lift the carb piston up by a mm or 2. When I do this the engine instantly cuts out.
Could it be fuel delivery. The fuel filter is full and when I open the float bowl there is fuel present. Or maybe an airleak?
Driving me crazy

[BoboGib]

when you lift the dashpot up where is the jet sitting? A good base level is to get it sitting flush with the carb body then go from there.

[n00b]

Ahh . . might be onto a winner here.

so as soon as the throttle is applied from idle it cuts out (lean)

naturely would run lean due to the airleak.

increasing mixture ie choke creates a richer environment,

id put my money down to an airleak. you say youve rebuilt the carb, im guessing you took off the inlet manifold if you have an aftermarket one.

Did you replace the gaskets and other seals surrounding the carb?

If so the inlet manifold could be fouling on something like the exhaust?

[chlblnz]

when you lift the dashpot up where is the jet sitting? A good base level is to get it sitting flush with the carb body then go from there.

When I took the carb to pieces on the weekend, the jet never reached that far up even when the mixture adjustment was at its leanest. It always had a recess of about 1mm into the carb body. Is this a problem. I have a number of different old carbs lying around and all of the jets do this.

[chlblnz]

Ahh . . might be onto a winner here.

so as soon as the throttle is applied from idle it cuts out (lean)

naturely would run lean due to the airleak.

increasing mixture ie choke creates a richer environment,

id put my money down to an airleak. you say youve rebuilt the carb, im guessing you took off the inlet manifold if you have an aftermarket one.

Did you replace the gaskets and other seals surrounding the carb?

If so the inlet manifold could be fouling on something like the exhaust?

I have the original manifold still on her. I replaced the carb gaskets and put some sealer around to make extra sure. It was happening before I took the carb off. I can see that the gasket between manifold and block is a little weathered. Would that have such a drastic affect on the running?

[n00b]

In aswer to your question . .YES lol

i once tried to fit a standard inlet/exhaist manifold which had been angle ground into the two and found the top of the gasket sat flush to the inlet. what i didnt see was that is was fouling on the lower side against the exhaust. (airleak)

Id recomend tightening the nuts that hold them in place, if not a new gasket will be in order perhaps.

ERic

[chlblnz]

In aswer to your question . .YES lol

i once tried to fit a standard inlet/exhaist manifold which had been angle ground into the two and found the top of the gasket sat flush to the inlet. what i didnt see was that is was fouling on the lower side against the exhaust. (airleak)

Id recomend tightening the nuts that hold them in place, if not a new gasket will be in order perhaps.

ERic

Ok. So took the manifold(s) off. Some clever little chap has cut them appart. This now means the inlet cannot be lined as it should as there are no indents in the flanges. Will look into getting a new alloy type.
I bought a new gasket. Came very quickly. All bolted back together and did as best job as possible with the inlet.
She now runs pretty sweet. Redid the timing. Fiddled with the carb. Still runs a little smoother with the choke slightly out but that could just mean it needs a proper tune. Also the s**ty old inlet might still not be completely lined up.
Thanks for all your help. Will keep you posted when the new inlet arrives

[n00b]

is very much what i happened to find on mine.

new allow inlet and job sorted

ERic

[n00b]

try this .

http://www.theminifo...ct/10878/cat/18



ERic