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  #31  
Old 4 Weeks Ago
smokey 2 smokey 2 is offline
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I have the same problem with my '70 xlch. It will go forever at 65- 70 mph, but
go to75 and it loses it. I will be checking all the tips on here this weekend.
Thanks for everyone contributing.
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  #32  
Old 3 Weeks Ago
Bigshankhank Bigshankhank is offline
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Quote:
Originally Posted by Tomcatt View Post
But this does sound like fuel starvation. To be sure (it is or isn't) disconnect your fuel line from your carb, put a measuring cup under the fuel line and turn on the petcock. To make 50 HP you need to flow an absolute MINIMUM of 5 gal of gas per hour. That means filling an 8 oz measuring cup in less than 45 seconds.

If you can't get at least 8 oz of gas out of the fuel line in 45 seconds you have a fuel flow problem. I rounded the numbers a bit but this will give you an idea if you have (or don't have) a fuel flow issue. BEST way to do this test is with the bowl off of the carb and measuring fuel flow into the bowl thru the needle and seat but flow out of the fuel line will give you an idea what's going on.

Interesting, the thread skipped to the next page and I missed this advice. I don’t disagree that this sounds like a fuel flow thing, but I’ve had a cracked coil on a bike that behaved erratically so once bitten twice shy I guess.
I’ve finally carved out some time tomorrow morning to go through some things on this bike and I will check this, I do love the process of elimination. Considering the reserve setting on the petcock does not function (leaving me hilariously stranded out of fuel the other night as a thunderstorm bore down on me) it wouldn’t shock me to find out that it is restricting flow.
Thank you!
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  #33  
Old 3 Weeks Ago
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Quote:
Originally Posted by Tomcatt View Post
But this does sound like fuel starvation. To be sure (it is or isn't) disconnect your fuel line from your carb, put a measuring cup under the fuel line and turn on the petcock. To make 50 HP you need to flow an absolute MINIMUM of 5 gal of gas per hour. That means filling an 8 oz measuring cup in less than 45 seconds.

If you can't get at least 8 oz of gas out of the fuel line in 45 seconds you have a fuel flow problem. I rounded the numbers a bit but this will give you an idea if you have (or don't have) a fuel flow issue. BEST way to do this test is with the bowl off of the carb and measuring fuel flow into the bowl thru the needle and seat but flow out of the fuel line will give you an idea what's going on.
This is a great idea. It may make a (slight) difference how full the tank is, so maybe drain a whole tank through and see if/when it slows down. Definitely test it on reserve too.

I've had brand new aftermarket crap like petcocks and tank strainers that were inadequate right out of the box. So just because it's new and clean, don't assume it should work.
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  #34  
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Did a simple test and pulled the fuel line off of the carb and dropped it in to a measured jar. In 18 seconds I got 12 floz through the fuel line, so fuel flow is not the issue.
Pulled the plugs and while the front one is whiter, both were dry and predominantly brown. I then checked compression on both cylinder and the front read 130psi while the rear only read 118. That’s not cool, looks like I’m in for a top end job in the near future.
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Within 10% of each other. I wouldn't be overly concerned.
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Adj the valves and do comp test again (@ WFO). Tight valve will not contact head properly and will not pass off heat to head. Perhaps you've been experiencing a valve sticking as mentioned prior.
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Are you using a stock ignition system or an aftermarket system? I have had this same problem and thought it was my fuel system and I checked out every angle of the fuel system and could not find anything wrong with the fuel system. Then I turn to the ignition system. Since I change my stock ignition system over to Dynatek long before I started having the same issues as what you're having. I decided to change the ignition system back to the stock ignition and the problem was resolved. So, I contacted Dynatek, told them my problem, sent it back to them and they replace it with a new system. I have the new Dynatek system install and everything has been running fine with no more issues.

Last edited by BlackThunderBolt; 3 Weeks Ago at 00:15..
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  #38  
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Quote:
Originally Posted by BlackThunderBolt View Post
Are you using a stock ignition system or an aftermarket system? I have had this same problem and thought it was my fuel system and I checked out every angle of the fuel system and could not find anything wrong with the fuel system. Then I turn to the ignition system. Since I change my stock ignition system over to Dynatek long before I started having the same issues as what you're having. I decided to change the ignition system back to the stock ignition and the problem was resolved. So, I contacted Dynatek, told them my problem, sent it back to them and they replace it with a new system. I have the new Dynatek system install and everything has been running fine with no more issues.
Haven't been able to open the iggy cover and research that.
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Quote:
Did a simple test and pulled the fuel line off of the carb and dropped it in to a measured jar. In 18 seconds I got 12 floz through the fuel line, so fuel flow is not the issue.
That's not a full test. The biggest restriction point in the fuel supply is always going to be the needle and seat.

You need to pull the drain plug ad measure fuel flow into the float bowl itself.

What you describe in your first post is VERY indicative of fuel starvation.

Unless your running Sifton Bonneville cams and open short drag pipes but I would expect serious hesitation in the other gears would have told you about that problem.

These engines require a lot more fuel than most people think. They generally only get about 55 miles to the gallon.
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  #40  
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Originally Posted by Ferrous Head View Post
That's not a full test. The biggest restriction point in the fuel supply is always going to be the needle and seat.

You need to pull the drain plug ad measure fuel flow into the float bowl itself.

What you describe in your first post is VERY indicative of fuel starvation.

Unless your running Sifton Bonneville cams and open short drag pipes but I would expect serious hesitation in the other gears would have told you about that problem.

These engines require a lot more fuel than most people think. They generally only get about 55 miles to the gallon.
Given more time, pulling the float bowl and testing flow through there is on the list. I did notice that while I had recently filled the tank with fresh gas, when I first disconnected the line from the carb the gas was brown. Once I opened the petcock the gas from the tank was normal yellowish. So it’s possible there is sediment in the bowl.
Again, lack of time.
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