Hi can anyone help me.

I have completed the build of my carb'd yamaha R1 Turbo Mac about 1500miles ago, it drives very nice and you wouldn't know of any underlaying problems that it had as I didn't until last week when I took it in for a rolling road tune.

Let me explain,

I drove about 40 miles to PDQ in Slough to get a roading road tune, the guy hooked it up to the rollers and gave it 3 good runs, after which he said to me the car is running dog rich so bad infact that the wideband sensor could not keep track of it and as soon as the car reaches 3000rpm the richness line goes way off the scale.

No problem he thought and changed the main jets to a more suitable size, checked the needle positions, fiddled with the mixture screws a little and then run it up again. This time the car was mega lean.

From that we though right we are on to something here the first jets 1.44 dog rich, the second ones we tried way lean 1.20 so lets try something in the middle so the changed the main jets to 1.32 smack bang in the middle.

Guess what it would barely run at all would rev a couple of times up to a max of about 5000rpm then cut out, would always start again though no probs.

We couldn't understand what the hell was happening.

We then decided to adjust the boost pressure on the turbo from 7psi upto 14psi (.5bar to 1bar) and every where in between but it made no difference (this engine has turbo pistons/rods/head studs/gasket etc) before anybody asks.

In the end we carried out 9 runs all of which were dog rich.

The rolling road guy reckons that the car has something else effecting the fueling a few ideas that he came up with was that the waste gate was sticking open and the car wasn't boosting properly, or the fuel pressure regulator was not working correctly. I personally thought that it maybe the fuel pressure regulator to fault but as of yet can't prove or disprove that, I have put a fuel pressure gauge in the fuel line and it does tick over at 3psi of fuel pressure which Jack Frost from Holeshot Racing recommends is the correct pressure, the fuel pressure does appear to rise quicker than the boost but they do end up at roughly the same pressure which will be causing a slight problem but not to the extreme that would cause such richness (i dont think)

I am about to change the fuel feed and return lines because at present I do believe that the feed line is a larger diameter than the return (feed 10mm) (return 8mm) I am going to put on a (8mm feed) and (12mm return) and ensure that there is no restriction at all in the return pipe as this is 1 of the possible culprits to this problem, if this still remains I am going to strip the fuel regulator and make sure the diapham is ok and all the other bits and bobs inside but after that I am stuck for ideas, I am very reluctant to think that it is the waste gate sticking however I may take a look if nothing else comes up.


Please tell me know if anybody else has any sensible ideas or possible causes.

Thanks in advance.

Fuel pressure needs to be a constant 1.5 - 3psi above boost pressure, if they are the same then it will not fuel at all.

Does not explain the richness, how are you pressurising the fuel bowl?

You might get some good suggestions here

To be be honest the engine was lift straight out of a bike that was built by Holeshot racing so all the pipe work was set up by them, the pressure to to the fuel bowls comes from the plenuim.

I was under the impression due to what I have been reading in other forums that the fuel pressure could be the cause of the richness do you not agree with that.

what are the needle std or have you got a dyno jet kit, also these over std jet sizes put in more fuel.

I had same issue on carb bird engine, when on boost very hard to control fuelling with carbs,

had to settle at 9 psi and ran a fuel pressre reg can t remember pressure but turned up a little to get it at about 13 afr which is still not great,

check needle position and if dyno jet ones go back to std

good luck

They are standard needles set at 1 away from the leanest setting clip 2, when you say that you turned up the pressure to get it to 13 AFR, are you saying that you turned the fuel pressue up?