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Puzzling PAIR related issue

Old 08-14-2012, 07:33 PM
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Puzzling PAIR related issue

Hello all,

I've been trying to avoid posting in case I recycle old news, but I cannot find anything to explain my problem so here I go. I've recently come into possession of a 2005 VTR1000F, much abused and neglected. Standard exhaust, unknown carb setup, PAIR removed, no vacuum petcock on the fuel system so it is just gravity feeding (got one on order). I have done 1000miles since buying the bike; it doesn't blow smoke, drop oil or dump oil in the airbox but I have used 1.5L in that time, so I smell more trouble.

The current problem: After finding that the PAIR check valves were not blocked off, I capped them. On starting the bike again, it fired up normally (read; takes a few cranks, idles for 30 sec then tries to stall on idle until the engine gets some warmth, that's another problem), but as soon as I give it some throttle, it died. I took the caps off the PAIR check valves and it is back to normal; idles and revs normally, the check valves draw a vacuum as though they are still functioning.

I've now flipped out the reed valves and found that one was flipped while the other was not (PO was clearly a bit of a space waster). I still can't think of a reason for the bike to be starving while revving with the check valves blocked, yet running well-ish with them vacuuming? I've currently got the tank and airbox off, so I can take pictures easily if it will help. I was hoping for something easy like PVLIR, but without a vacuum petcock... The first thing I did after buying the bike was take it to a mechanic for a major service and inspection; he just changed the fluids, filters, checked the valves, synced the carbs, charged me a fortune and told me "these bikes go forever, she'll be right."

Any ideas?
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Old 08-15-2012, 09:24 PM
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Thanks for the reply. The airbox PAIR hole is capped off, so no problem there. I understand that the PAIR should have no influence on the performance or power-production cycle of the motor, that it simply decreases the amount of unburnt fuel escaping through the exhaust.

That is why I cannot understand why my bike won't rev when the PAIR check valves are capped off? Why would a vacuum in the head during the exhaust stroke prevent the engine from revving? It would help if I could tell whether the inability to rev was due to fuel/air starvation or lack of spark, but I was not smart enough (or mechanically capable enough) to work that out before I pulled the bike apart.

That last line sounds a bit ominous, doesn't it? "Not mechanically capable enough" and "pulled the bike apart." Recipe for disaster.

All opinions appreciated!

Last edited by wrya1; 08-15-2012 at 09:28 PM.
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Old 08-16-2012, 05:14 PM
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[QUOTE=VTRsurfer;339973]Make sure all vacuum hoses related to the PAIR are capped, and make sure that the 2 large carb float bowl vent tubes (about 1/2 inch in diameter) are open and not kinked. They should also be angled down, if possible.

That sounds like a good idea. I will get onto it. PVLIR is not a possibility because I don't have a vacuum petcock, the bike was modified with an straight through gravity feed fuel line. The vacuum ports on the cylinders that would normally supply the petcock have been plumbed together.

I'll see if I can get some pictures up.
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Old 08-16-2012, 06:46 PM
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I had a idea from a mechanic friend that I am trying to nut out; he suggested that the bike could be flooding when I rev it if the throttle slides are not opening. They are operated via a vacuum on the carb diaphragm and if they don't move, the bike gets no air therefore it will run at idle but flood when the throttle opens.

Is there any way that the carburetor diaphragms would be affected by the change in vacuum that occurs when I block of the PAIR check valves?

Also, just to show that no news is new news, I came across this thread:
https://www.superhawkforum.com/forum...ont-run-28670/

Post #10 sounds like my problem

Last edited by wrya1; 08-16-2012 at 08:29 PM.
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Old 08-29-2012, 03:01 AM
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Progress

Well, after being out of town for a few weeks, I have thrown myself back at the VTR. Got a vacuum valve installed with a quick release between the tank and the valve so I can remove the tank but leave the vacuum valve in place (it is the later valve attached to the frame variety, not the valve on the base of the tank variety).

As a bit of a test, I capped off the PAIR check valves, hooked up the tank and the base of the airbox (didn't attach the stacks or the filter, wanted to watch the carbs), started up the bike. Just like in the past, it idled normal but did not want to rev. I tried with the choke on; would stall at 3500 with a spatter of fuel through the carbs and into the airbox, especially the front carb.

Turned off the choke, and things were a little different; if I grabbed a handful of throttle, the bike would stall the same as above. If I slowly built the revs, however, I could get to 7000RPM but no further. It would not stall at this level, however, just would not rev any higher.

With no air filter, the bike is getting a lot more air than normal. THis allowed it to perform a little better, still not right. Could it be flooding? The PO probably had an aftermarket exhaust, perhaps he had rejetted it and now with normal exhaust it is too rich... Better get on the jetting forum.
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Old 09-04-2012, 05:21 AM
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Running 178/180 mains, 45 pilots, AU1F/E needles. All very standard.
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