Hey all,
My issue is, carbs are running extremely lean on idle but not higher up the rev range, when I first start the car, AFR's are a touch rich but very quickly fall off to 20+ ahead of the car stalling (which means exceedingly lean if I'm reading the gauge right) Above 2000rmp through redline I'm 13-14AFR without any load, because the car has no front end on it and doesn't idle so I can't go for a drive.
I'll set the scene so you can have a better picture for answering, I converted my fuel injection civic D16 engine to bike carbs, changing in tank pump for a low-pressure unit from Merlin motorsport, I forgot the exact model because it was 2 years ago), have fitted a malpassi filter king with gauge and set the pressure at just below 3psi. I have changed the timing system so that it no longer needs an ecu (though is still fitted), it is triggered via an older D series vac advance distributor which has the base timing at the correct (middle) dot on the crank pulley and verified with a timing light. I have fit an AEM AFR gauge which is seemingly working as intended.
The carbs are r1-4xv mikunis which to my understanding are relatively large for a 1600cc though it's not unheard of especially on AFH engines in polos. I am using standard r1 carb joiners and clamps from mani to carb backs and well tightened. I have changed all the vac lines to brand new on the balance bar and to the brake booster with decent (tight) clamps to ensure no vac leaks, I have done the easy start trick around the base of the manifold to see if there is a vac leak there to no avail, gasket was new and fitted well.
I have double checked the floats are set at the right heights (I see one guy on the forums saying 4-5mm but that is what appears to be fuel level not float level, float level 6-7mm from sealing surface), ensured my carbs are balanced with a carb synch on the mouths and I checked the butterflies with feeler gauges down to .010 they all seem to be sucking in the same amount of air at 3000rpm.
Pilot jets are 17.5 which I believe is standard here and is what is advised. All jets are clean and clear having been removed umpteen times now. Mixture screws, I have tried everywhere between 1 and 5 turns out but I have the same problem. It just seemingly doesnt get enough fuel delivery on idle to keep it going, I can rev out of it no problem.
What I have noticed when pulling my carbs apart, the float heights when set on the valves (not decompressing the pins) seems to be in check. When the carbs are the right way up, the floats, and the amounts the needle valves are subsequently pulled down don't match from carb to carb. two of them go a few MM lower than the other two at full droop. I don't have an infra red thermometer to check exhaust temps to see if when it starts running lean it corresponds to the two carbs which the floats don't drop as far. I want to think my fuel pump is delivering the right amount of fuel because the level in the bowl of the reg doesnt go down.
Where would you start here? Am I barking up the wrong tree with the float droop? The needle valves appear in good order with decent spring in them. Get new mixture screw o-rings? I'm going to check my fuel pump is offering fuel pressure consistently because it could very well be that dropping off.
My issue is, carbs are running extremely lean on idle but not higher up the rev range, when I first start the car, AFR's are a touch rich but very quickly fall off to 20+ ahead of the car stalling (which means exceedingly lean if I'm reading the gauge right) Above 2000rmp through redline I'm 13-14AFR without any load, because the car has no front end on it and doesn't idle so I can't go for a drive.
I'll set the scene so you can have a better picture for answering, I converted my fuel injection civic D16 engine to bike carbs, changing in tank pump for a low-pressure unit from Merlin motorsport, I forgot the exact model because it was 2 years ago), have fitted a malpassi filter king with gauge and set the pressure at just below 3psi. I have changed the timing system so that it no longer needs an ecu (though is still fitted), it is triggered via an older D series vac advance distributor which has the base timing at the correct (middle) dot on the crank pulley and verified with a timing light. I have fit an AEM AFR gauge which is seemingly working as intended.
The carbs are r1-4xv mikunis which to my understanding are relatively large for a 1600cc though it's not unheard of especially on AFH engines in polos. I am using standard r1 carb joiners and clamps from mani to carb backs and well tightened. I have changed all the vac lines to brand new on the balance bar and to the brake booster with decent (tight) clamps to ensure no vac leaks, I have done the easy start trick around the base of the manifold to see if there is a vac leak there to no avail, gasket was new and fitted well.
I have double checked the floats are set at the right heights (I see one guy on the forums saying 4-5mm but that is what appears to be fuel level not float level, float level 6-7mm from sealing surface), ensured my carbs are balanced with a carb synch on the mouths and I checked the butterflies with feeler gauges down to .010 they all seem to be sucking in the same amount of air at 3000rpm.
Pilot jets are 17.5 which I believe is standard here and is what is advised. All jets are clean and clear having been removed umpteen times now. Mixture screws, I have tried everywhere between 1 and 5 turns out but I have the same problem. It just seemingly doesnt get enough fuel delivery on idle to keep it going, I can rev out of it no problem.
What I have noticed when pulling my carbs apart, the float heights when set on the valves (not decompressing the pins) seems to be in check. When the carbs are the right way up, the floats, and the amounts the needle valves are subsequently pulled down don't match from carb to carb. two of them go a few MM lower than the other two at full droop. I don't have an infra red thermometer to check exhaust temps to see if when it starts running lean it corresponds to the two carbs which the floats don't drop as far. I want to think my fuel pump is delivering the right amount of fuel because the level in the bowl of the reg doesnt go down.
Where would you start here? Am I barking up the wrong tree with the float droop? The needle valves appear in good order with decent spring in them. Get new mixture screw o-rings? I'm going to check my fuel pump is offering fuel pressure consistently because it could very well be that dropping off.
the carbs are mounted on a bogg bros manifold and the bottom seal does seem relatively well levelled
