Bike Carbs On Ax Sport

[robi1000 0]

Hi everyone!

 

I've finally got round to fitting my new carbs (R6 Keihin). Now I must set them up correctly. I would like to get them almost spot on and then go on the rollers where I could get exact info on AFR and then I could CNC some custom needles.

 

When I first fitted the carbs I drilled the jets to 1.6mm . Car idled fine and it felt fine up to 3000 rpm. After that it was just way lean and performance was disasterous. So yesterday I decided to drill the jets to 1.8mm. Now it pulls really strong on half throttle from 2000 to 4000 rpm. If I open the throttle fully there seems to be little difference. After that it doesn't pull strong anymore. It revs all the way to 8000 but it does not perform as it should. From 4000 upwards when accelerating on WOT it jerks a little bit as if it would be lean again.

 

When I dip the clutch revs rise a little bit (about 500) and stay there for about 3 seconds or so and then slowly fall towards idle. It's getting worse with higher revs. Anyone else with similar experiance?

 

I have to mention that I did not change needle position so it's possible that vacuum is keeping needles up and because of the size of the jets engine revs itself.

 

My spec now is:

 

1.3 TU24 bottom end

1.6 8V TU5 head, ported and lowered 0.9mm

original TU24 camshaft (I think it's about 270 deg duration)

Keihin CVH carbs (I think they are from the last R6 that was carbed)

 

Any ideas what should I do?

 

Oh and engine noise is absolutly fantastic!!! I think everyone should once own ITB'd (carb'd) car!

 

Cheers

 

Robi

[swordfish210 20]

I've replied to your PM now

[sub205 5]

[... lots of staff deleted ...]

 

1.3 TU24 bottom end

1.6 8V TU5 head, ported and lowered 0.9mm

original TU24 camshaft (I think it's about 270 deg duration)

Keihin CVH carbs (I think they are from the last R6 that was carbed)

 

Any ideas what should I do?

 

Oh and engine noise is absolutly fantastic!!! I think everyone should once own ITB'd (carb'd) car!

 

Cheers

 

Robi

 

pictures!!! ;-)

 

i have 2 big throttles from mikuni and plan to build me something to use them on my xu10j2 converted car.

 

have you tried installing a wideband lambda and monitored the mixture?

 

maybe this will give you a clue.

Edited July 8, 2009 by sub205

[robi1000 0]

@swordfish210: Tnx mate!

 

@sub205: I'll have to make a hole in the downpipe and weld a nut on it so I can screw wideband lambda in it... Until then I'll have to rely on my feelings.

 

Here are some quick shots I took while I was putting this together with a friend of mine. There's just a few of them because I was busy with conversion and my hands were dirty.

 

Here we go:

 

Inlet manifold

 

 

Before we tightened all the screws on the flanges:

 

There will be more after I put on my new cam cover. The one now on the engine is just provisional and is really ugly.

[meggy6620 0]

Hi sory diferent subject but is the engine mount strong enough naw youv altered it? I ask because im doing the same as you ish but for my rally car and im umming and rrring wether it will be strong enough as i dont want it to come loose or fall to bits when i go down the stage.

 

cheers steve.

[robi1000 0]

No problems so far and my car is driven really hard. Just be careful to leave as much strengthening ribs as possible.

 

Some pics for you how I did it:

 

 

 

 

 

 

 

These are all the pictures I have.

[meggy6620 0]

great thanks mate thats a great help ill keep the forum posted on haw my engine build is going

 

cheers steve.

[calvinhorse 870]

could'nt decide which shoes to wear?

 

inlet looks very nice

[robi1000 0]

Actually you're right! When I bought my shoes I really couldn't decide wheter I should choose black or white laces... And then I decided I should try them both for some time till I decide. Now I prefer black ones, but I'm too lazy to change them.

 

Here are some vids of my car:

 

First run:

 

THE noise! (It's not set up right yet so it's not as fast as I'd want it to be - yet)

[robi1000 0]

I have a problem I can't solve.

 

After I have fitted my new carbs I've tried to set them up so that the car would go at least as fast as with double solex. I've set the mixture screws on the float bowls 3 turns out. And then I've tried jets sized from 150 to 200!!! on a 1.3 engine. With 180 jets it was ok up to 4k, and then there was no power again.

 

Then I've tried blocking that hole on the front of the carbs (under the trumpets) that is in line with the needle. I gues thats main air jet? Anyway that improved things a bit and car gained some power, but with size 200 jets it was overfueling (doh...).

 

Today I've taken the plugs out of air jets and tried to do something with the screws on the float bowl. First I've tried with two turns out and it was not ok. Then I've tried with four turns out and it wasn't ok either.

 

Now I've ran out of ideas what to look for. No matter what I did my car wasn't bogged down in lower revs. A lot of people must drop their needles two notches down so that the fueling in the lower revs is right. So how come my car is running fine and pulls fine with size 200 jets?!? It's just the opposite of what I'd expect.

 

If anyone has any idea what to do, please share!

 

 

Cheers

Robi

Edited August 12, 2009 by robi1000

[unariciflocos 49 1 Cars]

I found a guide on tuning bike carbs here , but didn't have time to follow it.

 

My main jets are 1.8mm and I'm running quite lean over 5000 rpm. Tried to blank out the air correctors under the trumpets and the engine was just spitting half the gas out the exhaust. I then used a soldering iron and a thin drill to make hole smaller than normal and it was still over fueling down the rev range but no noticeable improvement over 5k rpm so i just returned them to standard size.

 

I'm hesitant to increase the main jets and don't know what to do with mine either and i was thinking of ditching the whole carbs thing and go back to std injection since i'm only running 150 bhp on an mi16.

 

Don't know what to say about yours but 2mm main jets sounds like a lot. Maybe you could get a jet kit and try experimenting with different combinations.

[robi1000 0]

Yeah I know that 2.0 jets are a total overkill for a 1.3 engine. But I was so desperate and I've tried with that also. With blocked air correctors, my car was also spitting out fuel through tailpipe. Not to mention the smell of fuel.

 

I just can't understand how people just fit their carbs, drill the jets a bit and everything works fine?

 

People who have bike carbs: How many turns out are your mixture screws on the float bowls set?

 

What kind of needles are you using. Do you use original fuel return pipe or did you block it off? Any changes on other jets or air correctors? Any changes on floats?