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GTX 657 Mikuni carb rebuilt kit
- Thread starter Mazachs
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AKnarrowback
Well-Known Member
No......
ONLY USE GENUINE MIKUNI CARB KITS.
You will hear this a million times on this forum. Mikuni costs more, but for a reason. They are worth every cent.
ONLY USE GENUINE MIKUNI CARB KITS.
You will hear this a million times on this forum. Mikuni costs more, but for a reason. They are worth every cent.
https://www.amazon.com/gp/product/B01BHI8G68/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I used this seller on amazon and was satisfied to find that they were genuine mikuni
I used this seller on amazon and was satisfied to find that they were genuine mikuni
AKnarrowback
Well-Known Member
Non mikuni parts will let the machine run, but it won't run right. This just leads you down the road of searching in all different areas for a solution to your running problems when the peoblem is in the carbs.
Mazachs
Member
I did my carb rebuilt on my GTX 95 with a genuine Mikuni kit. The ski starts very well. The grey hoses on carb were replaced with black car fuel line. The other ones will be replace later (during the winter). To avoid to have debris from those grey hoses i put a fuel line filter at the jonction with black hoses. No leaks, all pressure tests are perfect. The pop-up is equal on both carbs at 22psi. I did "on water" test drive. I have hesitation at mid range. Low speed screw are 1-1/4 out. High speed screw are 1/4 out. Does anyone have an idea what could be the cause of that hesitation? What do you suggest to adjust or look at?
describe the hesitation in more detail.
The reason I ask is because different types of hesitation can lead to different causes.
My first assumption with the hesitation is that your low needles are allowing for slight flooding. In this case, you would hesitate until higher RPMs. At these higher RPMs, you will be burning enough fuel to overcome the flooding issue. So ultimately the question is if you put the throttle all the way down does it jump up and take off like you'd expect it to.
The reason I ask is because different types of hesitation can lead to different causes.
My first assumption with the hesitation is that your low needles are allowing for slight flooding. In this case, you would hesitate until higher RPMs. At these higher RPMs, you will be burning enough fuel to overcome the flooding issue. So ultimately the question is if you put the throttle all the way down does it jump up and take off like you'd expect it to.
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Ckrawiec
Well-Known Member
If you have not replaced all the grey fuel lines to black automotive lines, just selective replacement, you are asking for trouble....so just be aware of that.
The inline filter will be RECOMMENDED to be removed as it is a potential leak source and it restricts fuel flow.
Mid range hesitation COULD possibly be caused by the Rave valve blades...see attachment for reference....I am NOT suggesting this is the cause...just passing along some info for thought....it's probably just a carb issue potentially....the pop-off pressure might be a tad low....I think I remember someone posting that they dialed in a POP of 27/28 and that was ideal (for THEIR ski)....just throwing out ideas here for consideration....
The inline filter will be RECOMMENDED to be removed as it is a potential leak source and it restricts fuel flow.
Mid range hesitation COULD possibly be caused by the Rave valve blades...see attachment for reference....I am NOT suggesting this is the cause...just passing along some info for thought....it's probably just a carb issue potentially....the pop-off pressure might be a tad low....I think I remember someone posting that they dialed in a POP of 27/28 and that was ideal (for THEIR ski)....just throwing out ideas here for consideration....
Attachments
second on that statement. if you don't change them all your still going to eventually be pushing slime through the carbs
Mazachs
Member
I agree with you, the grey line will be remove soon, they were just kept as temporary. This is why I add inline filter between the grey hoses and the black ones to avoid debris to go inside the carb. I'll try to remove the grey hoses this week-end. About the pop, i'll try to raise like you suggest. By the way, i don't have rave valve on this GTX 1995. It's only a 657x.
About the hesitation, it’s between 1/2-3/4. At WOT, it’s good. If i release a bit the throttle to 1/2 and put it back to full, it’ll hesitate a bit and after that it rev perfect. I took a look to the plugs, they are coffee brown.
About the hesitation, it’s between 1/2-3/4. At WOT, it’s good. If i release a bit the throttle to 1/2 and put it back to full, it’ll hesitate a bit and after that it rev perfect. I took a look to the plugs, they are coffee brown.
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Mazachs
Member
After read carb adjustment tips, i understand the function of each part depending of the throttle position. According to this, i thing my issue could come from the high speed screw or the high speed jet. It looks like i have too much fuel at 3/4 until it reach full. Before to change the high speed jet, i will try to lean the high speed screw. Both are at 1/4 turn as factory setup.
Agree with Mikidy. The factory recommended settings an jetting including pop off settings will result in a perfect running engine. Both my 657s and a pair of 657xs my cousin has run absolutely flawless. Original Mikuni parts and follow the book. Get rid of all the grey line and thoroughly clean the entire fuel system. If your pop off doesn’t check within spec you either have the wrong springs because someone changed them or one or more is bad which is rare. The original Mikuni springs rarely fail. I didn’t read all the replies but I assume your compression is in spec ?
Yes check your compression and make sure you have a good verified compression gauge. It only takes s small amount of lost compression to give you a slight throttle lag.
So an interesting story on this. I rebuilt two 94 GTXs. One I ordered a complete engine rebuild kit from a guy who sold on eBay. He had good parts and the kit had a rebuilt crank and fresh cylinders with new pistons rings and all the trimmings. Keep in mind the 94s were plain 657s. No X. Long story short is he sent me fresh 657x cylinders which are different. With this kit you reuse your old head which is also different. There’s been much debate on here about what’s different between the X and non X and I found out the hard way. On the X motor one of the changes made was to make the cylinders taller by ten or so thousands. Then the head was shaved down by the same amount to maintain the same squish or compression. So if you look at a non X head it will have a small step up to where the domes start. In the non X the top ring f the pistons came clear to the top of the cylinder wall at TDC. Word is this caused some heat distortion issues so they changed that on the x motor. So long story short is if you have X cylinders with a non X head your compression will be about 20 psi low and you will have a slight part throttle lag. Took me a summer to figure this one out. Also just FYI NEVER mix non X cylinders with An X head. Catastrophic failure is eminent. Rule of thumb, always check squish clearance when rebuilding a 657.
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