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VFRJake

'93 won't rev past 5000rpms

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Hi all,

 

Looking for some help. I was out for a ride last week and had trouble starting after filling up with gas.  I had been dealing with a hot start issue (starter clutch) for a while, so I thought it finally gave up the ghost. I changed that out along with a clean air filter and new plugs. There's no more grind with hot starts, but I'm still having a hard time starting the bike. Instead of the choke, it seems to fire up if I hold the throttle wide open when starting. It will idle and run fine up to about 5k, maybe 5500, and then fall on it's face. So, what's supposed to happen at 5k rpms that isn't happening? Carb issues? Electrical issues? Other ideas?

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inspect the sparkplugs to see if too much fuel is getting into cylinders, may be leaky float needle.

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Not sure if this helps but - Have you installed the correct temperature range plugs? And could your crappy ethanol added fuel be causing issues? (if you're using ethanol fuel that is?). Have also heard of High Octane Premium fuels causing havoc with older carby bikes, fouling plugs.

Whats the state of your Fuel Filter?

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Measure Vac (from the stator) and Vdc (RR/battery)  outputs with the engine hot while you are at it.  Just to rule electrical out.

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Is your sub air cleaner filter still intact? Might have been sucked into the carbs causing these issues.

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Could be

 

blocked or blocking air box inlet or clogged air filter.

 

High fuel level in carbs or some other cause for over fueling when the carbs transition onto there main jets.

 

Could be clogged main gets. The hard starting could indicate the carbs need a clean or balance or there is a vac leak.

 

Check the plugs, see what colour they are and how. Much carbon is on them. Or whether they are loose?

 

Give it a rev with the air cleaner out of the box.

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Howdy,

 

Thanks for all the suggestions.

The plugs looked old but not terrible, maybe a little dark/rich. Fuel filter is new. Air filter will be cleaned and oiled (K&N). Sub air cleaner is intact. 

 

I have the carbs pulled but don't know exactly what I'm looking for next as I've never worked on carbs before. Sure have gotten to smell a lot of gas though. If anyone can point me towards a carb-newbie resource or walk me through what's next, that'd be great. 

 

 

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53 minutes ago, VFRJake said:

Howdy,

 

I have the carbs pulled but don't know exactly what I'm looking for next as I've never worked on carbs before. Sure have gotten to smell a lot of gas though. If anyone can point me towards a carb-newbie resource or walk me through what's next, that'd be great. 

 

 

vfrw has a good carb cleaning thread. use proper tools, don't be careless as carbs can be damaged easily. if you want professionally-done work, box the carbs and send them to me, good results guaranteed. i have a set of gen3 carbs just rebuilt with new O-rings and bowl gaskets for sale and ready to go for $300 + $18 shipping.

91116_008.JPG

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Another question because the bike is stored an hour away and I can't mess with it right this second.

 

The previous owner rigged up this very innovative pinch bolt setup for one of the throttle cables. Is the cable that comes over the top 'push' or 'pull'? I had to cut the cable to get that nonsense out.

 

20190622_162950.jpg

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16 hours ago, VFRJake said:

The previous owner rigged up this very innovative pinch bolt setup...

Hot start troubles, and needing to open the throttle for starting seems to indicate an overly rich condition.

 

Hmm, the routing of your throttle cables looks completely wrong. The bracket should locate the cables ahead and in-line with the pulley on the carburettors. Can you post a photo(s) showing more of that area?

 

This photo from Reviving a 1994 VFR750F shows their orientation. Note this is from a '94 VFR and the service manual indicates some differences  between the '90-'93 and the '94-'97 models. It appears the throttle shaft rotates clockwise so the lower cable opens the throttle and the upper one closes it. There is no push function with the throttle, the second cable is just a braces & suspenders back-up should the throttle spring be unable to close it.

 

throttle_cables_carb.jpg

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3 hours ago, Lorne said:

Hot start troubles, and needing to open the throttle for starting seems to indicate an overly rich condition.

 

Hmm, the routing of your throttle cables looks completely wrong. The bracket should locate the cables ahead and in-line with the pulley on the carburettors. Can you post a photo(s) showing more of that area?

 

This photo from Reviving a 1994 VFR750F shows their orientation. Note this is from a '94 VFR and the service manual indicates some differences  between the '90-'93 and the '94-'97 models. It appears the throttle shaft rotates clockwise so the lower cable opens the throttle and the upper one closes it. There is no push function with the throttle, the second cable is just a braces & suspenders back-up should the throttle spring be unable to close it.

 

throttle_cables_carb.jpg

Yes, I was thinking rich as well, but not sure why. The cables are all goofed up in the photo because I removed the bracket that holds them in line and was trying to get the top one through that bolt area. I need to buy a new top cable, and they seem to be listed as either push or pull when I search. I'm guessing pull is correct and pull = open.

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