Hybrid fuelling

[plodder]

If I give my 4/6 full throttle at low revs, it does fcuk all until about 4K and and then as the revs go up it starts to pull properly at 7K and then it's off.

I've not got access to a dyno, so help me out here as to what I should be changing. I'm currently thinking needle needs raising a bit but wanted a second opinion.

[Evilchicken0]

No idea at all butu up to 6000 is pilot jets.

Raising the needles sounds like the thing to do and that's what I'd look at first then if it doesn't work or the topend suffers maybe try a size up on the idle jets

[plodder]

Got the carbs off today and the main jets are #112. (the pilots are #35 as per the spec)

The Yamaha service manual says #118 for the main jets.

The question is: Will increasing the size of the main jets back up to #118 richen it up all the way through the rev range or only at the top end? I'm not 100& clear because althoguh the needle jet restricts what comes from the main jet, there is an emulsion tube that mixes in air before it gets to the needle, so I wondered what effect this would have.

Any carb experts?

[cagiva996]

Hi plodder im no carb expert but my hybrid (pre t/cat motor) with the 95 foxeye motor ran ok with 115 mains and the needle on its weakest setting.the bigger jet will make it run richer as soon as it comes on the needle,then right to max revs.though you may be running a different airbox set up to mine(3tj airbox with 600 carb inlets plastic welded underneath to fit carbs,3he k&n filter,fz750 airbox inlet and tank raised)i had many troubled hours setting the carbs up with different jet sizes and needle positions.the fzr600(4jh) airbox is quite a bit bigger so make sure your getting enough air to the airbox to start with as if you aint flowing enough air it wont run sweetly enough to make any usefull changes,the tj airbox struggles to provide enough air for the bigger motor,though this is only personal experience and i think other hybrid builders havnt got a problem.i think i made a mistake when made the airbox and didnt elongate the airbox holes enough for the airbox to fit snugley under the tank and the intake snorkel is too close to the underside of the tank.also check the float heights as this can also cause problems
http://www.factorypro.com/tech_tuning_p ... gines.html" onclick="window.open(this.href);return false; try this cv carb set up guide as this is what i used when i insalled the factory pro jet kit and had some good advice-best of luck

[plodder]

I'm running a 3TJ airbox with the holes enlarged and the sides of the air box melted in a bit at the sides to get it under the tank. I zip tie the front mount down to pull the whole air box down and run with no snorkel (the filter is held in with wire across the top). The front of the tank is also raised by 12mm by rearrangin the front mount rubbers and putting in a bit of 6mm MDF.

I pulled the needles up form middle to bottom (richest) today and it was must worse. It didn't want to start also I had to open the idle screws up to 2.75 turns but still had a flat spot off idle. Horrible it was. Needless to say it was the wrong way to go (there's a pun in there somewhere).

So I've gone to one from top on the needle but not had a chance to test it. Still flat just off idle so it's at 2.25 turns out, whic seems to make it better.

I was also thinking about making a hole or holes in the bottom of the air box below the filter centre to draw in air from the gaping void below the box but not got that far yet.

[cagiva996]

I tried the same thing taking the airbox snorkel off and holding the filter in with wire,but no matter what jet/needle combo i used it had a nasty hole in the power and i couldnt adjust it out.i think to work properly the tj box needs to keep its lid and trumpet on.i used an fz750 snorkel/airbox lid-it only needs a bit of trimming but you need a couple of self tappers to keep it in place its intake trumpet is larger than the tj one and lets in more air.you could try taking the filter out and stretching a peice of stocking/pair of tights under the intake lid and another peice stretched between the airbox halves.this was an old trick used on tuned 2 strokes that needed to lose the filter but keep shit out of the box(ooeer!).ive used this on my hybrid with the t/cat motor and it works very well so may be worh a try-you get lots of air but no hideous induction roar as well.dont give up!!!

[toosmooth]

if anyone needs an FZ750 lid and snorkel, I just happen to have one in the garage...

[plodder]

Tested it last night and it's much better. Still a bit of a hole at WOT but easy to ride around i.e. pootling about at low revs doesn't need much throttle and then gunning it just drop it a gear & go (keep it above 6K).

Maybe I can get it better on the lowest needle settng but it's pretty good now.

Toosmooth... how much are you wanting for that FZ750 snorkel? If it's not too much that I could see what it does.

[toosmooth]

the whole replacement airbox owed me £28 (I only needed the rubbers), you're having a bit less than half of it, allow 3 quid for postage, lets say £15 delivered to your door and we have a deal.

toosmooth

[Alex.]

Well, my hybrid seems a little out of the ordinary!

For the airbox, I enlarged the holes for the carbs and then elongated them to allow the airbox to sit further down towards the rear and blanked off the gaps. Then I took the trumpet off the top and left just enough plastic to hold down the standard filter. The tank would not fit, so I cut down the carb rubbers to allow the airbox to sit even lower, although the clamps holding the rubbers onto the carbs have nowhere to clamp. Now the airbox fits under the tank with the filter.

She runs just fine! Top end is ballistic and the mid/low end is fine except a bit rough. When I got the engine/carbs they had short bellmouths, very short. With these bellmouths the midrange was much rougher, but still rideable, standard bellmouths improved the delivery no end. I must be lucky as there are no flatspots or dips in the power delivery.

I don't know if the engine is standard, but the carb settings are standard needles, pilot jets and emulsion tubes, but the mains are 135s.

I really must get to a dyno.

Alex.