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1990 VFR750 Running/Starting Problems


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I have a 1990 VFR750 with some running problems, I'm looking for some help with this bike.

First I'd like to add some backstory to this bike. I picked up this bike for a trade (rode for an hour to get it) and when I got it I got a chance to ride it. When I went to make the trade the bike would stall out about 10min after riding (but could punch it and get it up to 11k rpm and into 3rd and fourth gear) and the previous owner kept having to jump start it.

He drove an hour to me (swears he had no problems up till the trade) but owner did let me know that he picked it up from someone who let it sit for a year. 

When riding for about 5-10 minutes the bike won't throttle over 5000 rpm and as soon as you let in on the clutch and throttle it would die.

I put in a new battery and after about 10min of the bike running with choke on i was able to ride it with the choke off. Went and rode it for about 30min with a friend and it only died twice and i kept having to mess with the idle screw, sometimes it would idle at 4000 sometimes would feel like it was about to die.

I had a friend come take a look at the bike and found that it had a aftermarket rectifier and fuel pump in it and the intake for the bike was partially tied shut with what can I only assume is hobby wire. 

As of right now with fresh battery it will only run with choke on at 1000 RPM as soon as you touch the throttle it dies. 

I have done some basic checks:

  • All connections for charging system are clean and not burnt.
  • I reinstalled the correct rectifier SH701-12 (owner said that was on the bike originally) 
  • Runs at 12.06 volts at 1000 RPM and it gets to 13.03 volts at 3000 RPM and seen it peak at 14 at 5000+ RPM (It is at 11.8 volts at 1000 RPM now I think I killed the battery starting the bike multiple times)
  • Reinstalled original fuel pump
  • Ran some mechanic in a bottle through the gas tank to help the carbs 
  • Engine oil is clean and at a good level.
  • Low on clutch fluid
  • Air filter is clean
  • No hissing when idling 
  • All fuses are okay 
  • New AGM Super start battery

It dies whenever I touch the throttle or idle screw it dies, I'm thinking bad stator or clogged carbs.

Has anyone had this issue or can lead me in the right direction.

 

20200810_013042.jpg

20200812_172943.jpg

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First of all, nice bike.  Every time I see a 3rd gen (rarely these days) my reaction is "oooh - look at that 8 spoke wheel! 

 

You have a lot of things to sort out - here are some things to think about in order. 

 

First, if it were mine I'd try to undo all the "mods" the previous owner(s) did to get back to as close to stock as possible, starting with the wacky airbox thing  :blink:.  Then be sure you have a good fuel pump. 

Second, I'd next attack the carbs, making sure that you have good fuel in the system.  Being 30 years old, there could be all sorts of crud, deposits and varnish in the tank, fuel filter, pump and carbs.  You can at least empty the tank (and have a look down in there to see how clean things look) add some fresh fuel and then drain the carbs to get known good fuel through the system.  If there's a lot of rust, jetsom and flotsom in the tank, you're likely in for cleaning that out and a new fuel filter at least.  Clogged jets would not be a surprise - you may need to bite the bullet and rebuild the carbs, either having it done or DIY'ing it.  If the latter, there are some members here that are really sharp on going through 3rd and 4th gen carbs (I wish I were one of them). 

Lastly once you have it running well, your charging system seems a bit weak.  You likely have at least decent stator output as you're getting some reasonable numbers at 5,000 rpm, but you should really go through "The Drill" in the electrical forum to thoroughly assess the stator, R/R and wiring.  Repair / replace as necessary and you should be good.

 

That's not a lot of help - there's likely some very knowledgeable advice that will follow.  That is a now rare and nice looking bike that deserves the attention needed to get it going - once you do you'll really love it.  I wish more 3rd gens were around - but they've become a fairly rare site. 

 

One other thought - you mentioned that it's low on clutch fluid.  It would be good maintenance to change both clutch and brake fluid - since it's low it sounds as though it's been neglected and it would not surprise me if the fluid looks like the gravy you'll put on your Thanksgiving turkey. 

 

Best of luck with it and update us on how you're doing with it.

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Welcome to VFRD from across the pond!

 

To add what was written already, you can run the bike without the fuelpump by the way

IMG_20200807_161706.thumb.jpg.2ac3d5d5daa0a2647dffee2c6d5faf52.jpg

 

 

 

 

Check that the 4 vacuum ports are sealed; I believe the 3rd gen could have little screws, where the 4th gen have capped "boost joints" #5

image.png.db49fa704337c594d5ebad2119510faf.png

 

 

IMG_20200809_120142.jpg.78aa85884ec2923fde3405fa3c95b6eb.jpg

 

IMG_20200809_125809.jpg.652970f251c762f6a20b66e1c5f7e92e.jpg 

 

 

 

Before going through the hassle of removing the carbs, verify synchronisation;

This for instance is not bueno

414456887_IMG_2449resize.thumb.jpg.680b7120c314c1cc1b24b704a35394a4.jpg

 

 

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I recently found a great carb kit company outta texas in the US for all the carb parts for the V-4s.

Great service, complete kit and good communication. I"ll try to find the name and get back to you.

 

If you decide to rebuild the carbs (and i'd recommend it if you are keeping the bike).  the top tier kit is pricey at $150 bucks or so but worth it in the end.

 

Wish i could remember the name.

https://billysoutback.com/carburetor-rebuilds.html?mode=list

 

 

 

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Joe @v4dreams.com has a photo study in dealing with the carbs, I rebuilt my RC24 carbs recently and that was a major part of my toolkit 

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I pulled the carbs and in the process of cleaning them, everything is a little crusty and gross.

I did find this video with a 1995 vfr that had the same problems and she does a good job explaining how to remove and clean the carbs.

 

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I used to have have a specialist VFR motorcycle business in the UK back in the mid to late 1990s, so did alot of these. However was a while ago now and am a little rusty but will see what I can remember.

I think everything has been mentioned that you need to check to be honest. The charging system on the RC24s are prone to failure as the regulator/rectifier is not really good enough, so keep an eye on that side of things. And also the emulsion tubes in the carbs should be changed too, they may look ok but they can be an issue. And as mentioned, strip and clean the carbs, especially make sure the jets are clean and diaphragms not damaged or squeezed. Soak overnight in brake fluid and they'll soften up and come right. If they are hard or not fitting properly could explain the poor running when you try and open the throttle. And always balance the carbs when the engine is warm. From memory the front left is fixed, the others you adjust to match that one. Cooling pipe running at the bottom of the V is an issue, so make sure you cover it to save burnt hands! Oh yes and of course, get rid of that mickey mouse mod to the airbox!!!!!

Good luck with it. I have a 1988 VFR750 I bought new and still have, just covered 220,000 miles and stripping it down to check it over. Needs rings, maybe! What a great bike and very underrated in this era of speed and technology. If they are looked after, they'll do the miles no problem. 

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On 8/13/2020 at 9:36 PM, TheOneNewman said:

Low on clutch fluid

 

You might find a leak in the clutch slave. Fluid will show up running down the kick stand. Just one more job. Not too expensive or too difficult.

 

You already dug into the carbs. That's the right way to go. If you had been lazier, I'd have suggested starting with sea foam. It's controversial, but my own experience with a situation similar to yours is that it worked. The recommended amount added to a full tank of fresh gas, and then a repeat with a second tank with the same additive before things just smoothed right out. I'd been ready to do the rebuild so I was delighted to save myself the bother.

 

It looks as if you're doing great. Beautiful bike.

 

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Carbs will be going back together as soon as I get my float gaskets. I do plan on making my manometer, there are only 2 places in my city and they charge 100$+ depending on how off your bike is. I used to work for a supercar dealer in the repair department so this should be simple. The only thing I'm worried about is that front right carb access because it's right up against a cooling system split and kind of a pain to get to.

 

I'm going to drain the gas from the tank and when the bike is up and running I'm going to run a mechanic in bottle through it. 

 

I wish the tubes between the carbs were metal and not plastic. 

 

Definitely going to change the spark plugs with all the problems I've been having. I do see a leak of some sort but haven't had a good chance to look for it. I need yo pull the bottom cover and give the bike a good wash.

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  • 2 weeks later...

So I cleaned the carbs and everything was mostly clean. Just some dried ethanol but I used some crc carb clean and blew everything out and made sure the carbs stayed as balanced as possible (didn't even move the screws). I did remove the stock air screw adjustment caps and make sure they were 1.5 turns out from tight. 

Put the carbs back on the bike and .... still doesn't start.

Messed around with it for a while, got angry and went to lunch.

After lunch and some thinking I pressed the kill switch on accident and noticed it didn't make a difference starting with the kill switch on or off.

I pulled a spark plug and my spark plug is not burning off the fuel.

So some electrical testing needs done.

Wondering if the kill switch went bad.

20200823_204816.jpg

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Got it running, after some extensive testing I couldn't figure it out. I was getting ready to call my dealer and give them my kidney. I called my local parts store and ordered spark plugs and tried to order a fuel filter, and the parts guy said "I can't find the fuel filter let me make some calls". So I looked in the repair manual and the fuel filter is in the gas tank, I pulled off the metal "directional" fuel filter. Started right up no problems, now I have to find an oil leak somewhere near the rear exhaust.

 

The thing that gets me is that the fuel bowls were getting fuel and the fuel line was spraying gas (not super hard) so I guess there has to be enough fuel to the bowls. 

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On 8/14/2020 at 2:55 AM, Dutchy said:

Welcome to VFRD from across the pond!

 

To add what was written already, you can run the bike without the fuelpump by the way

IMG_20200807_161706.thumb.jpg.2ac3d5d5daa0a2647dffee2c6d5faf52.jpg

 

 

 

 

Check that the 4 vacuum ports are sealed; I believe the 3rd gen could have little screws, where the 4th gen have capped "boost joints" #5

image.png.db49fa704337c594d5ebad2119510faf.png

 

 

IMG_20200809_120142.jpg.78aa85884ec2923fde3405fa3c95b6eb.jpg

 

IMG_20200809_125809.jpg.652970f251c762f6a20b66e1c5f7e92e.jpg 

 

 

 

Before going through the hassle of removing the carbs, verify synchronisation;

This for instance is not bueno

414456887_IMG_2449resize.thumb.jpg.680b7120c314c1cc1b24b704a35394a4.jpg

 

 

Love my Morgan Carburetor Tool!

 

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On 8/26/2020 at 4:55 PM, TheOneNewman said:

Got it running, after some extensive testing I couldn't figure it out. I was getting ready to call my dealer and give them my kidney. I called my local parts store and ordered spark plugs and tried to order a fuel filter, and the parts guy said "I can't find the fuel filter let me make some calls". So I looked in the repair manual and the fuel filter is in the gas tank, I pulled off the metal "directional" fuel filter. Started right up no problems, now I have to find an oil leak somewhere near the rear exhaust.

 

The thing that gets me is that the fuel bowls were getting fuel and the fuel line was spraying gas (not super hard) so I guess there has to be enough fuel to the bowls. 

The fuel filter is not in the tank on the RC36; it is on the LHS of the bike, like in Dutchy's pic (which is of a 4th gen, but it's very similar).  Which manual are you looking at?  There is a copy of the American Honda one in the Downloads section.

 

Charging voltage is tested at 5,000rpm, and 14v is within spec (13.5v-16v @5,000rpm), and you should see over 12.7v from a healthy, fully charged and rested battery.  OEM reg/recs on this model usually fail, btw, so OEM is not what you want in this instance.

 

Ciao,

 

JZH

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