Need carb advise. Pumper carbs.!

Carbonfibre said:

Cant really advise without any information on the numbers related to the new cam, or how the timing was checked. But in some cases where intake depression at idle is reduced by a longer duration cam, if you have OKO carbs then drilling out the air correcters (small holes in carb intake throat, that will be revealed when pilot screws are removed) will often correct poor idling.

Wonder where you bought the carbs from though, as I would have thought that the seller should be able to help with this, as if the problem is linked to the carbs then its probably something that has happened before? I have noticed a few people selling the OKO carbs have been removing the OKO branding from the carb bodies, and selling as Keihins though, and not sure whether you are likely to get much help from a seller like this.

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The reputable Californian I got these from is very helpful, along with others. Fiddling is a given, patience takes more work and much practice. I never assumed that i was going to bolt these on and go on down the road, but i was hopeful.
Needle-ing, jetting, balance tubing, orifice drilling....you know all the usual stuff.
A smooth idle was also not expected, in fact I kinda like a lumpy, cammy idle if it's really from a hot cam rather than just a poor runner.
I have yet to fire it up with the balance tube in place. I will see how that goes before further voiding any warranty(already much too late for that).
HAS ANYONE ELSE DRILLED OUT THIS HOLE THAT CARBONFIBER SPEAKS OF? Not that I don't believe, it is a little drastic.

Whether it's OKO or Keihen is rather moot at this point.

Very easy to tell whether or not its Keihin or OKO.............the OKO's pretending to be Keihins have the OKO branding linished off, and the word "Keihin" is not likely to be seen on doctored OKO carbs.

Its not something that really matters as the OKO's work very well indeed, but here in the UK are less than a 1/3 of the price of Keihins.

Carbonfibre said:

drilling out the air correcters (small holes in carb intake throat, that will be revealed when pilot screws are removed) will often correct poor idling.

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Is this the hole that you speak of? Am I at risk of irreversible damage?

Not a good idea to try modifying the carbs unless you are able to work out whether they are OKO or Keihin.

Carbonfibre said:

Not a good idea to try modifying the carbs unless you are able to work out whether they are OKO or Keihin.

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What is the difference? These are listed as " Keihin/PWK Twin Carb Kit" on the JSMotorsports web site. Now, where do I stand?

No personal experience but if Jim Schmidt is holding them out as Keihins, I strongly suspect they are just that.

You shouldn't need to do any drilling to get them to work. Once the balance tube is in place you will need to re-adjust the idle and mixture screws. Adjust them with a warm motor. You know it's right if it runs like shit cold without the enrichener. If the balance tube helps with your bad spot but doesn't completely get rid of it you can drill the balance tube fittings larger. Depending on the cam and compression ratio you may need to go up to about 3/16 hole. I have used 1/4 inch ID on rare occasions. Jim

pvisseriii said:

Carbonfibre said:

Not a good idea to try modifying the carbs unless you are able to work out whether they are OKO or Keihin.

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What is the difference? These are listed as " Keihin/PWK Twin Carb Kit" on the JSMotorsports web site. Now, where do I stand?

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The difference is that the OKO carbs are about 1/3rd of the cost of Keihin, but more to the point its difficult/impossible to advise on how to go about modifying a carb without knowing what make it might be.

On the UK Keihin importers web site there is no mention of the PWK32 (http://www.allensperformance.co.uk/products-pwk.html) so its probably safe to assume the carbs you have are OKO.

If they are OKO these carbs often respond well to having the air correctors drilled out very slightly using a 1mm drill. This is very easy to do and takes about 1/2 hour, but its not the type of job for anyone not confident with using hand tools, as its possible to ruin the carbs if you are clumsy.

Before doing any modifications though, I would advise checking the jetting, and float height, as OKO carbs often come from Taiwan with float heights not quite right, and if you have the parts inside the carbs they wont work no matter what mods you might do.

Carbonfire -

Jim Schmidt/JS Motorsports is about quality and he stands behind his stuff.
They aren't OKOs; they are PWKs. I bought a set from Jim too; that's how I know. Not speculation, personal knowledge.
Coupled with a Tri-Spark ignition unit, my '73 750 runs beautifully without hesitation or hickup at any engine speed.

I wasnt aware that Keihin made 32mm PWK's...............The carbs shown on the JS web site are OKO copies of the smaller body Keihin PWK 28mm carb, with a slightly larger body which can take the larger 32mm choke size.

Nothing in the slightest wrong with OKO carbs, and the quality is pretty close to the genuine Keihin products. However anyone who removes the OKO branding, and sells them for the same price as Keihins is not particularly honest, as they are only about 1/3 of the price of the Japanese carbs!

This is getting a bit confusing Pvisseriii, What carbs have you got on at the moment ? I think you said that you were getting close with the Amals.. Idle was better after you modified the idle tube and fitted the # 30 Pilot jet, and was then going to try # 35... How did it go... Also # 3.0 Slides. I still think it's too much cutaway and should try # 2.5... Something to keep in mind... The distance between clip settings on the Needle can be extreme, Sometimes a small shim washer half that, placed under the clip will be sufficient to lift the Needle enough to remedy a leanness problem. Hang in there, it's all forgotten once it's right... AC.

Carbs pictured on the JS site are OKO's with the OKO branding linished off the side of the carb body. If the guy is getting these direct from Taiwan his unit cost is going to be around $25 per carb, so looks like a very nice profit to be made here!

Well then, good for Jim!

IMO anyone going to the trouble to develop and sell products into this niche market should make huge profits. :mrgreen:

The OKO carbs cost around $25 each, and maybe less if you are able to deal direct with the factory in Taiwan. Just doesnt seem to be very honest removing the OKO branding, which is likely to suggest to buyers they are made by Keihin (who incidentally dont make 32mm PWK carbs!).

As to "development" not much seems to have gone on if posts from forum members with these carbs fitted are accurate, which is a real shame as properly jetted and set up OKO carbs are far superior to OE Amals. and cost considerably less money if not bought from the man with the linisher!