Types of Mikuni/ Solex 44

[Gregs672000]

Thanks for the info. Do you know anyone that has shims to adjust the floats? Carb say n44phh-a11 on side but it looks to be using 40 jet blocks and air jets. As you pointed out do not see an external float adjustment. Also a bit weird as it’s has 180 air jets outboard and 165 on the inside throats.

I wonder if someone was using exhaust temps to set up the carbs. The variation in air jets is significantly different. Individual cylinders can run at different temps, but is pretty involved to get data while on the mains without a dyno and lot of sensors.

[gtrbg]

The car is a mixture of Datsun performance parts and stock. Car had the remnants of a BRE style side exhaust that I had rebuilt. Not sure if that might be part of the explaination?

Dave - Thanks for the info and carb parts.

[Gregs672000]

The car is a mixture of Datsun performance parts and stock. Car had the remnants of a BRE style side exhaust that I had rebuilt. Not sure if that might be part of the explaination?

Dave - Thanks for the info and carb parts.

Just guessing here, but it makes sense to me. How old is the set up? If you think about what might be available to measure things, exhaust temps are a known indication of what is happening in that cylinder from an air/fuel standpoint I think, and more accurate than a wideband in the collector reporting an average of 4 (?). With a laser temp gun now available and on a dyno maybe that could be done too? Or maybe they just read the plugs after holding it on the mains only (high RPM) for a long time and found this was a better balance? Just spit ballin... never seen that before. Or maybe they are drilled out 165 to 185 and you don't know it... so many fun possibilities! Ha!

[gtrbg]

David

Thanks for the help and parts. Car significantly better with shim for float level and jets. Went a bit higher on pilot and turned down pressure.

Significantly better on right hand turns but still get a little bog but much less than before. Before I drill the carburetor I heard a dam inside the jet cover helps between jets and vents.

[Gregs672000]

Dave's the man!

[gtrbg]

So problem of right hand stumble mostly fixed by Dave’s recommendation on float level and jets. Did have a little bit of remaining bog and one of the Datsun 510 racers with Mikunis who had added vents through the float bow cover by putting in a brass right angle fitting and piping mentioned some old racers effectively put a small aluminum wall extension adding to the existing low wall. This can be done without drilling the cover. I found some thin wall aluminum piping that I cut with a pipe cutter and filed to a tight interference fit. Will test at the next race. If it doesn’t work it is easy to remove. If it works than I do not have to cut a hole in an original float cover. Will update.

[theunz]

Please keep us informed of your progress. I’m experiencing the same issue and have adjusted my floats after talking to Dave a few weeks ago, but the last autocross got rained out and I haven’t been able to test the adjustment. I too would prefer not to add a vent if possiable.

[rwmann]

Creative block!

If it’s ‘too much’, you could drill through the tubing to provide a small amount of relief flow.

[gtrbg]

Ordered tubing online and kit had an assortment of tubing of various sizes that fit inside each other. So have assortment of sizes if one is to big a block. Hope to test next weekend.

Adjusting the float per Dave’s measurements fixed almost all the issue. So hope this can reduce the bit of bog that is left. I only get the bog after a high speed right turn after a straightaway. You might be ok with just the float adjustment hopefully.

[gtrbg]

Still a little bog so not sure if helped. Was at Thomson which is a very windy course.

[SLOroadster]

Still a little bog so not sure if helped. Was at Thomson which is a very windy course.

Is it a bog, or a full on stumble? Bog could simply be a tuning issue. If it falls on its face when you get on the power, that is the vent issue. Are you running a wide band O2? If you are, is it going lean or rich? I can't seen what pilot jets you are running, but based off the jet blocks, you have homogeneous carbs. There are two schools of thought on how to set those up. The most common says to run smaller air correctors with little tiny fuel jets. (say 140 fuel, 130 air). This might work on a street car, but will lead to amid- high rpm lean condition on throttle tip in. I tried and tried to make this setup work, and it simply wouldn't on my engine. I went back to the independent type setup where you take your fuel jets and add 30 to find your air jets to get into the ball park. I think I ended up with 155 fuels and 180 airs (can't remember off the top of my head) but in street testing, it looks and feels good. I do need to get the car out on track for some track testing, just haven't gotten there yet. I will say I'm running 41mm venturis in a set of 44s as well. With this setup the small jets were almost undrivable due to lean stumble.

Will

[gtrbg]

The big stumble was fixed by Dave’s suggestion on float level reset and jets. Could see it was going way rich on air fuel meter before that fix. After that fix there is just a a bit of a burble and was seeing if I could remove with a bridge under the cover rather than drilling a vent in my original float covers. Cannot really tell if the bridge helped at all since different track with tighter turns. May fine tune float level again. The current set up I can deal with unlike the major bog that occurred before.

[CSP311]

Mikunis do have one flaw in them that only comes up if you are racing with a high flow head. The carbs will flood the vents and cause the engine to hack and gag on the fuel flowing through the air jets, and other places where it shouldn't be. It only happens through right hand corners however. It clears up as soon as the car is returned to straight line running or a left turn. The fix is to seal off the vents under the jet cover and drill a new vent in the top of the float cover at a high point. I had to have this done on mine.

Looking at these (below) from the google translate it seems to help with the cornering G (force) fueling...? The difference is more holes in the jet block. Is this the same thing?

https://www.jauce.com/auction/s1131283722

[david premo]

I’m fairly certain that the extra holes in the jet block are of no value and may be counterproductive. The jet block in the picture is a heavily modified OA or OB jet block and attached is a picture of the OA and OB blocks next to each other. If you look closely you’ll notice just below the threads the holes are different sizes and are smaller on the OB. The reason is the smaller holes are to enrich mid throttle mixture. It works on the same principle as the main air jet.

[Solex68]

I have a set like those jet blocks with the extra holes in them but I have never tested them out. Mine were from Kameari Engine works. But I have not tested them.

Kameari Emulsion Tube.jpg