Sidedraft Carb Questions

[Inka’d02]

I am running 40 mm DCOE side drafts on a fresh motor. I have a rough idle with and zero power under load. I am running standard Bosch plugs with a petronix equipped mechanical advance distributor (30 degrees advances at 3000RPM). I think it may be getting too much fuel due to the fact the plugs are fouling fairly quickly, they smell like gas and there is a gas residue in all 4 throats of the carbs. Not to throw another wrench in but I get an intermittent pop out of the exhaust. Would the rough idle and lack of power be a result of too much fuel and what might be the cause.

Any help is always appreciated

Thanks,

Andrew

[andrey]

Check all the jet sizes

[ahlem]

You should identify which jets you have and what your cam is to help give better info. How did you set the timing?

[Preyupy]

If you are seeing a lot of fuel in carb inlets you should first check your float level. if you are running the Brass Floats set them at 8.5mm plastic floats at 12.5mm (measure with the gasket in place with the floats hanging and just touching the needle, not compressing the spring!). Fuel Pressure needs to be checked, no more than 3 psi! Total advance should be closer to 35-36 deg. Do you know what jets are in the carbs? Are you running velocity stacks? If not do you have sleves installed to support the auxilary venturies? There are a lot of things on a Weber carb that can be changed to "JET" it for each individual engine. Chokes, Auxilary Venturies, Emulsion Tubes, Main Jets, Air Corrector Jets, Accelerator Pump Jets, Inlet Valves, Idle Jets, Float Level are the most common. They don't just bolt on and run great unless you have ALL of the correct pieces in place.

There are a lot of people on here that have a lot of Weber knowledge if you can tell us what is in the engine, Displacement, Camshaft, Compression Ratio, Exhaust system, Ignition,Air Cleaners, Velocity Stacks etc I am sure we can give you some idea of where to start on the "JETTING".

[Inka’d02]

Stock cam,

Main: 130

Air: 170

Idle: 50f8

Pump jet: 40

needle valve: 200

Aux ventu: 4.5

Main ventu: 30

Emulsion tube: F11

ANSA Exhaust

Short velocity stacks

9.5:1 compression

ramflo foam air cleaners

[Preyupy]

For a start I would try:

Check float level

Check fuel pressure

Idle Jets 45f9

Emulsion Tubes F9

Main Jets 125

Air Correctors 190

The Chokes and Aux Venturies are ok but that size choke is going to be all done making power by 5200-5400 rpm. The small chokes will make better torque at a lower rpm but will restrict HP at the top. I would recommend 34 mm chokes if this is going to be a track toy. If it is just a street car the 30mm chokes might be your best choice depending on how you drive.

The rough idle is most likely the idle jets, retarded timing and possibly the carbs are not balanced. Do you have some kind of Carb Syncing tool? Check between the #2 and #3 throat to adjust the linkage between the carbs but then check between the thoats of each carb often the shafts have been twisted by someone putting linkage pieces on and not supporting them correctly while they tighten the nuts. If they are twisted you need to straighten them out before it will idle correctly.

[Inka’d02]

Thanks!

I just checked the float levels they look good, I need to get a gauge to check the fuel pressure and I'll start looking for other jets.

[Preyupy]

with a 200 float needle and seat you should be able to get away with 2-2.5 psi fuel pressure. much more than 3.5-4 psi and the floats can be pushed down just by the fuel pressure and with engine vibration it is very hard to maintain the correct fuel level.

[TobyB]

Your jet/ choke numbers are close enough to start-

as Byron said, check the fuel pressure, and start troubleshooting

EVERYTHING else before you bother with the jetting/choking.

It should run very well (if not optimally) with those numbers.

Things like sync, bent throttle shafts, plugged idle passages,

shoddy shi**y misdrilled Spanish carbs, that sort of thing...

and do spend time with float level- try lowering it, and see if it

responds to that....

hth

t

[Scott Sislane]

I am running 40 mm DCOE side drafts on a fresh motor. I have a rough idle with and zero power under load. I am running standard Bosch plugs with a petronix equipped mechanical advance distributor (30 degrees advances at 3000RPM). I think it may be getting too much fuel due to the fact the plugs are fouling fairly quickly, they smell like gas and there is a gas residue in all 4 throats of the carbs. Not to throw another wrench in but I get an intermittent pop out of the exhaust. Would the rough idle and lack of power be a result of too much fuel and what might be the cause.

Any help is always appreciated

Thanks,

Andrew

When was the last time the carbs were used? And on what motor?

[Inka’d02]

They were on a 510 , running a year ago, i think.

[Scott Sislane]

They were on a 510 , running a year ago, i think.

is it possible that fuel was sitting in them for a year or so?

[Inka’d02]

fuel pressure is holding steady at 2.2, and no change with float height variation. I would be inclined to agree with the shafts being an issue but it runs so poorly under a load as well. I really don't want to run this thing much, I'm afraid I'm going to wash out the new rings

[Inka’d02]

They were on a 510 , running a year ago, i think.

is it possible that fuel was sitting in them for a year or so?

Maybe but I did a full rebuild on them before i put them on the car.

[Scott Sislane]

If you've exhausted all the suggestions from others (who probably know more than me) you may need to strip them down and put them in an ultrasonic cleaner. Sounds very similar to what I just went through. I ended-up installing new set after 3 months of chasing my tail.