I am asparatically challenged

Irish · Full Member Joined: Jun 12, 2007 Posts: 250

I have read too much and listened to too many fools, to the point now where I know less than I did before. So I will start fresh.
1975 xs650, pod type air filters, unrestricted exhaust. New coils/wire/condensors/plugs. Carbs have been taken apart and cleaned twice
Starts easy, runs good up to 55-60, everything falls apart after that. 5000rpm+ spudders, breaks up, loses power at high speed. My plugs look good, nice even tanish color. I use ngk b7es. I have heard every thing from it needs a bigger main jet to the air cleaners. I frankly haven't a clue.

INXS650 · 650Rider Supporter Joined: Mar 22, 2007 Posts: 645

Try next size up main jet. Sounds like it is starving for fuel up high. May want to check float level again as well.

TeeCat

Irish...

If it makes you feel any better, I look forward to being where you are now. My bike runs and idles nicely, but I'm not ready for that first road test yet. INXS is likely right - fuel starvation - and you should be good to go soon! Sounds like you're almost there!

TC

LouC

If you have any inline fuel filters, make sure they are not getting clogged.

At the higher rpm's, the fuel needs to be able to flow unrestricted. So the float level check is a good idea...if the bowl is getting emptied faster than it can be refilled, you'll have that kind of problem.

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

MIne was running great - no problems at all - then wham - it started sputtering at 5k too. My guess (hope) is it is just a clogged fuel filter or restricted line. Putting new in tonight will let you know.

bluebikerblan

Just a check on the quick and easy's......(you've probably already done it)
Vacuum petcocks?.... In line fuel filters?..... Tank gas cap vent?
Quick and easy check......take in line filters out if present. petcock valves on prime and leave tank cap cracked open. Give your high rpm run check.

Vacuum leaks -barb, hoses, petcock gaskets,plugged tank cap venting and or in line filters further restrict flow. It sounds like one of those situations where 1 plus 1 plus 1 might equal 6.......BOL Blue

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

I totally agree - and you bring up a good point - I put in a new gas cap seal yesterday - perhaps my problem isn't the fuel filter or line - but rather a restricted vent - which was made worse by a new seal on the gas cap!

mcat · Full Member Joined: May 10, 2007 Posts: 34 Location: omaha

check the vent in gas cap. mcat

Irish · Full Member Joined: Jun 12, 2007 Posts: 250

I did the tank vent before anything else. No filters. And my petcocks are worn enough that there is always fuel flowing ! lol It has now come into 40-50 degree weather here in the northeast so my spring project/summer ride has become a winter project again. Maybe next season....

What size main jets would you guys recommend?

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Could be the change to pods - you may need to re-jet the carbs - if it is falling apart at 5000+ try (lean) going up on the main jet a size or two. Also check your spark plugs - a bad plug will also fall apart at higher rpms.

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Yamaha xs650