Pulling 750 carbs is actually easy

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Freddy
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Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Pulling 750 carbs is actually easy

Post by Freddy »

Often seen it stated in this forum that pulling the carbies and refitting to a 750 is a horror job. After having done it now a few times, and worked out the best approach, I've come to the conclusion its actually a very easy job if approached the right way. Yesterday I took them off, cleaned, fitted larger main jets, set the fuel level heights, and refitted all in an easy days work.

And the main trick is to remove everything that gets in the way of free and easy access, or will get caught up. That includes the left hand coil, voltage regulator, and clutch cable, and vacuum balance tubes. Just spend the extra time removing all these extra difficulties that have to be worked around and the job is so much easier. It's still a time consuming task, but not a difficult one.

And with all this stuff removed, resist the natural inclination to pull the carbies down to get them out. They go in and out much easier if removed and inserted in the space above the rubbers. Pull them out and up, installation the reverse. And lightly rubber grease the inside of the eight rubbers, makes a world of difference.

P.S. And if you use a mains electricity work light, make sure the lead is no where near the hot exhaust when your engrossed syncing the carbies. It was quite a spectacular fireworks show.
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

And for what its worth, the one size bigger main jets in a D1 make a significant difference. Yes, the carbies were completely cleaned, and the slides polished etc, which would all make a difference, so its hard to separate out each bits contribution.

But the extra grunt when you roll on the gas is very noticeable. The D1 stock uses size 82 main jets in cylinders 1 and 4, and 85 in cylinders 2 and 3. I just moved the 85's to the outer cylinders and fitted new 88's to the inner cylinders.

The reason for just one size bigger is because I feel I could confidently do that for a performance improvement knowing no way would Kawasaki have tuned the bike for max power. So just going up one size was a pretty safe bet, probably could have gone up 2 sizes safely. When the back tire is getting worn I'll take the bike to a dyno and see what it say about the AFR and if I can go bigger.

Genuine Keihin jets in all the relevant sizes are freely available from a specialist shop in the USA. About $7 each and $15 postage to Australia. Took about 2 weeks to arrive.
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

Just gave the bike it's first decent long test with the larger jets. Absolutely no doubt it runs better across ever part the rev range. The slight hesitation/stumble that the bike has always had when you quickly rolled on the gas is all but completely gone. The hesitation when you just give it a little throttle to take off from the lights is also gone.

Today's test was conducted with the air temperature around the 35C (100F), at sea level, with 34% humidity. For this reason I don't have a doubt people in more moderate climates running at or near sea sea level could go up 2 sizes in jets without any problem.

With Sydney's temperature generally in the mid 20's C I reckon I can safely go up one more size so plan to swap the 88 main jets to the outer carbies and put 90's in the inner two. I'm actually not going to muck around shimming the needles etc. because I'm quite happy for the bike to be tuned toward the economical size in the cruise range.
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Richard
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Re: Pulling 750 carbs is actually easy

Post by Richard »

I somehow missed this topic but this is actually very worthwhile to know. Seems like apart from the new idle jets I also have to order two main jets :P
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

Richard wrote:I somehow missed this topic but this is actually very worthwhile to know. Seems like apart from the new idle jets I also have to order two main jets :P
I'll keep you updated on the jet changes and results.

So far my D1 is running 1 size larger main jets (#85,#88) with a noticeable improvement over the stock sizes (#82,#85). A couple of #90's are due in the mail in the next few days. I plan to go on a moderate distance group ride Saturday to 'lock' the current performance in my brain, and assuming the #90's have arrived on Sunday I'll move the #88's to the outside cylinders and the #90's to the the inners, and retest.

I've also ordered a couple #92, and a couple #95. I'll just keep increasing and retesting one size up at a time using the 'roll-off; full throttle method and see what happens.
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

Pulled, rejetted (up a further size to #88, #90), and refitted the carbies again this afternoon.

Total time to do the job, 90 minutes. That's completely disconnecting the bank and doing the task on the workbench. Thought about leaving the cables connected and doing it with the bank still hanging on the bike, but decide against that as again with the correct methodology it's about a minute job to disconnect and reconnect the three cables.

Total 90 minutes work without any fuss, struggle, bleeding fingers or frustration. The point I'm making is that with the right technique and approach removing the carbies, cleaning, and refitting is a piece of cake. It's just that you have to do it a few times to figure out the technique and methodology (which I'm happy to document in detail if someone wants to know).

I'll post up the results of the jet change after a test ride. Might be tomorrow, but the very hot weather is still forecast to hang around for a few more days yet.
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

Report after today's test ride with #88 and #90 main jets. Definitely going in the right direction. The 'bog' when you crack open the throttle full fast is reduced, but still evident (I'm aware CV carbies don't respond immediately as the slides need to rise). And the slight acceleration when rolled back from full throttle is reduced, but also still present. No introduced problems over the original stock jets.

So as soon as the two #92 jets arrive from the USA out the carbies will come again and the exercise will be repeated with #90 and #92. I plan to always keep the one size bigger jet in cylinders 2 and 3 because I believe Kawasaki have done this because these cylinders run hotter and hence the bigger jet for additional cooling.

The reason I'm laboriously working up one jet size at a time is to identify when to stop. Would be easy to put in say 3 sizes bigger, but how would I known that 2 sizes bigger would have done the job??
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Richard
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Re: Pulling 750 carbs is actually easy

Post by Richard »

Thanks for the feedback, following this closely myself. I wonder apart from millage getting less would there be any other disadvantage...?
Freddy
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Re: Pulling 750 carbs is actually easy

Post by Freddy »

Richard wrote:Thanks for the feedback, following this closely myself. I wonder apart from millage getting less would there be any other disadvantage...?
I'm not altering the 'cruising' ranges i.e. low or mid-range at all, so aren't expecting any appreciable drop in fuel consumption. The main jets really come into play in the last 1/3 of full throttle.

Today's ride was with #92, #90's. I don't believe it went as well as with the #90, #88 so they are going back in.

I'm also waiting on 4 new emulsion tubes for a C1 which I plan to try. The D1 in most jets sizes uses a different emulsion tube to the C series (and the Swiss and Swedish D1's which also uses the C1 emulsion tubes). The C's and Swiss D1's all appear to be fitted with bigger jets and all use this different emulsion tube.

So I'm going to fit the C1 emulsion tubes with the larger jets and see how it goes.

P.S. Bit of emulsion tube theory. They aren't just a tube with a series of holes randomly drilled in them to let air in to emulsify the fuel. The size and placement of the holes is critical in keeping the AFR constant across the range the main jet is operating. The fuel level around the emulsion tube changes depending on the throttle position, closing or opening more holes in the emulsion tube as the fuel level falls or rises in the tube due to vacume. This allows more or less air to enter the emulsion tube so alters the AFR to keep it somewhat constant across the throttle positions the jet operates. So the number and placement of those tiny holes in the emulsion tube is an important tuning valuable.

P.S. I've got pulling the carbies out, changing the jets are fitting with the bike ready to ride down to about 1 hour. I though about replacing all the bowl screws with Allan head screws so the bowls could possible be removed and the jets changed with pulling the carbies out. But the middle two would still be fiddly to do so is probably still going to probably take 30 minutes. So reckon just pulling them right out is still the easiest, if not just a little more time consuming.
Shedman
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Re: Pulling 750 carbs is actually easy

Post by Shedman »

I'll only pull the carbs if I need to for maintenance as I'm not too bothered about performance, I'm happy if she just runs nice. I find it nice and easy to push/pull the airbox rubbers in to the airbox for the extra clearance. I remove the filter box as well so I can get my hand inside to pull the two middle rubbers in and the outer two push in easily, fitting the carbs is just reversing the procedure. I've no idea how long it took me to fit the rack today but at a guess I'd say about 20-25 minutes without breaking a sweat. Ok, so both the inlet and airbox rubbers were new today but I've done it before in around the same time when they weren't.
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