750k wont pull at low revs

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BAZ
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Re: 750k wont pull at low revs

Post by BAZ »

How did you balance the carbs Dude
jordihutch
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Re: 750k wont pull at low revs

Post by jordihutch »

It was just a static set up I done. Making sure they were starting to open at the same time. Set mixture screws by the book. Float heights ok etc. Have not done any other synchronising . Cheers.
lairdofsmoke
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Re: 750k wont pull at low revs

Post by lairdofsmoke »

As usual the normal basics have been covered very well, but having read through a couple of times now, as it came from USA has some changed the sprocket ratios, k model should be 15 front 47 rear and 108 links. Sprockets have the teeth numbers stamped on them, so no need to count, hopefully. Could be worth a check.
On fragrant cloud
jordihutch
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Re: 750k wont pull at low revs

Post by jordihutch »

Hi , Not that either I am afraid , new chain and sprockets fitted as well. Can’t remember the sizes at the moment , but it was th recommended sizes everyone suggested on the forum. Cheers.
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raysunners
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Re: 750k wont pull at low revs

Post by raysunners »

Have you checked ignition timing?
jordihutch
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Re: 750k wont pull at low revs

Post by jordihutch »

:tw Hi , I am sure it was set up correctly when the engine was put back in the frame after the rebuild about a year ago . I put slightly bigger idle jets in it before the winter, after a suggestion I had , I am putting them back to standard again, probably this weekend as that made no difference . Cheers
teazer
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Re: 750k wont pull at low revs

Post by teazer »

That suggests timing or carbs, or really low compression - if everything else is STOCK and OK. I would go back a couple of steps and do a compression test and let's see if those numbers are much different to spec. That's best done warm, so fire it up and see if it fires easily with choke on and does it idle cleanly when the choke is closed. Then try adjusting teh idle mixture (air) screws and see if that makes any difference at all.

BTW, are they stock carbs or replacements? Please attach pictures if not sure.

It almost sounds like the inlet port timing is excessive. Did you measure the ports and port timing when it was apart? You can do a quick and dirty with pipes and inlets off with a degree wheel set carefully to TDC using a piston stop and then see when the intakes and exhaust start to open/close. We can compare those numbers to stock and to various tuned motors to confirm if they are stock.

And do you have any pictures of the pipe it arrived with? 3 into 1 pipes tend to flatten top end but are usually close to stock at low to mid revs. I have three different designs here and two are quite quiet, so that makes me wonder what the PO did to the bike.
jordihutch
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Re: 750k wont pull at low revs

Post by jordihutch »

Hi , thanks for the suggestions . I may have to contact my mate again who builds engines as a job , he might be able to answer some of these questions as has more of a clue about some of this.
I am sure it has standard carbs ( have always wondered if they are ok internally) as you can only clean & rebuild what you have.
I don’t know about porting being standard or not, it’s not something I had thought about much . I don’t know the make of the 3 into 1 it had on , but it was very loud.
I may have to leave this a couple of days till I get in touch with my mate again.
Thanks for all the help so far, hopefully we can get to the bottom of this at last. Cheers.
teazer
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Re: 750k wont pull at low revs

Post by teazer »

As long as he understands two strokes and what makes them tick, you should be OK.
jordihutch
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Re: 750k wont pull at low revs

Post by jordihutch »

That’s part of the problem, he has not working on 2 strokes for many years. He builds and tunes race engines for super bikes, super sports etc , but nothing like the GT 750. But he does know his stuff. Cheers.
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