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faulty pressure sensor


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I'm still trying to get my bike running.. I bought it recently with a seized engine after it sat a while.. I got it idling but it would not rev without bogging and popping out the carbs. after a new set of spark plugs and doing the Pea shooter and the Shotgun, and finally removing and cleaning the carbs (I did find a lot of crud in the bowls and clogged jets in the jet blocks), it still will not rev without blowing fire out the carbs (running without the airbox, I'll try it with the airbox but I'm sure it's something else as it's just too bad). It does run better but still seems like the timing isn't advancing.. So now I'm wondering about the TCI or the Pressure Sensor that rules the timing advance in the TCI. any thoughts? I've already checked compression and leakdown so I don't think it's valve lash.

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Gary-

With the bike running, have you looked down into the carbs and made sure the slides are moving? Checked the diaphrams for holes?

 

Check the mixture screws and reset them out 2 3/4 turns. Turn the sync screws out so the butterflys are not adversely effected and re-sync the carbs (I'm hoping you can a high enough RPM to do it) - this is also verify that the vacuum ports on the carbs aren't plugged.

 

Dave

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Another thought.

Since you found a lot of crud in the carbs, how is the fuel filter. Plugged? Broke and not filtering? Could there have been crud in the lines and once you put it all back together it blew all of the crud into the carbs?

 

Just guessing out loud here?

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I don't have an answer but what are the pea shooter and the shotgun?

 

Shotgun is a method of clearing jets and some internal circuits on carbs without dis-assembly.

 

I just did it to Tweety a couple of weeks ago and it cleared up a very annoying backfire on 1 cylinder in 3-4000 rpm range.

 

http://vmax.lvlhead.com/tips/shotgun.htm

 

This air gun from Harbor Freight is also very helpful.

 

http://www.harborfreight.com/pistol-grip-blow-gun-68259.html

 

Link to youtube video showing pea shooter.

 

 

Gary

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  • 2 weeks later...

good input randy on the pressure sensor. I figured it just drops the advance when vacuum drops rather than causing the engine to advance with rpm. My ebay replacement pressure sensor is also 2.3v at 1atm but only goes to 0.8V at 26 inches HG. My old pressure sensor went to 1V at 26 inch HG. the manual says it should go to 0.5V.

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When you said before the timing wasn't advancing I'd assumed you checked it with a timing light. The engine will run quite nicely without timing advance, it just has no power.

 

You're timing may be off, but it won't be the pressure sensor. It's job is to retard the timing when pressure is high (low vacuum).

 

Incorrect valve timing can also cause it. Your most likely reason though is it's lean, and running without the air box will make it lean.

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I'm pretty sure this bike ran at some time. The timing can't be off unless the rotor slipped or the tci is humped. and it does idle and on the timing marks so the timing is on. the PO seemed straight up and said it used to run and then he lost the clutch (leaky slave) and perhaps the carbs got gunked up from sitting. I went through the carbs. and yes, I checked timing through inspection hole. it just bounces around but doesn't advance. and the tack is sometimes erratic dropping out completely and otherwise it won't rev up (even turning throttle up slowly) past 2500 rpm without backfiring fire out the carbs. I've had the airbox on after doing the carbs (I think) and that didn't help. Guess since I'm locked up with this TCI (can't get it out yet, seems I have to pull the right and left fairings), I'll put the airbox in and try it buttoned up. I have to make some progress today just to rule that out.

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I'm pretty sure this bike ran at some time. The timing can't be off unless the rotor slipped or the tci is humped. and it does idle and on the timing marks so the timing is on. the PO seemed straight up and said it used to run and then he lost the clutch (leaky slave) and perhaps the carbs got gunked up from sitting. I went through the carbs. and yes, I checked timing through inspection hole. it just bounces around but doesn't advance. and the tack is sometimes erratic dropping out completely and otherwise it won't rev up (even turning throttle up slowly) past 2500 rpm without backfiring fire out the carbs. I've had the airbox on after doing the carbs (I think) and that didn't help. Guess since I'm locked up with this TCI (can't get it out yet, seems I have to pull the right and left fairings), I'll put the airbox in and try it buttoned up. I have to make some progress today just to rule that out.

If the tach is dropping out, you at a minimum have electrical and/or TCI issues.

 

Tach runs off #2 coil circuit. Tach dropout indicates this cylinders coil is firing intermittently.

 

Gary

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