750 rc36 don’t go over 9k rpm

[Peka]

Hello all, 

recently bought VFR750FL 1989. Great bike! except... doesn’t run above 9k rpm. Do you have suggestion what could it be? Carbs possibly? Today I check fuel hose, had a hole in it, so I fixes it. Also, I check if fuel filter, and it is not clogged. I check air filter, seems fine, but I’m going to replace it, since now I only cleaned it with air pressure. 

 

any comments, or suggestion would be great!
 

if you want, more pictures are coming 👍🏻

[squirrelman]

carbs mos likeli, one or more bad slide diaphragms or dirdi main jets

[Peka]

thanks, I will check it

[Dutchy]

As this bike is new to you and you are checking anyway.....

 

Remove seat and verify the the battery cables are firmly attached.

Measure the Vdc over the terminals idle and at 5000rpm.

I assume you have a multimeter. Remove tail fairing, in the right hand side you will find the voltage regulator. Unplug it, you should see 3 yellow wires on the plug. Measure resistance (ohm) over each pair/combination.

Start engine (preferably already well warmed up) and measure Vac over each pai/combo of yellow wires. The measurement should rise when you increase rpm.

 

The above is called "the drill" you can search for it on this forum.

 

This may not be contributing to your issue, but having verified the electrical system gives peace of mind

[Dutchy]

On the airfilter, an aftetmarket from for instance louis.de is a lot cheaper than Honda OEM.

Brand name is "Delo"

[Peka]

Thanks Dutchy. 
 

Today I’ve cleaned carbs and check membranes, they are fine, and carbs are nice and clean. 
but now it goes worse than before??? Previously, on neutral I could rev u to 11,500 rpm, now it is stucked to 9 even on neutral. 
 

checked sparkplugs, I would need to change them, but I need to order them, and air filter as well. 
 

regarding regulator, previous owner put brand new OEM, as he told me, and It is working great! 
 

Question for sparkplugs: do I need to remove fan and coolant, in order to change front sparks?

[Thumbs]

It’s running rich .....so did you check the float height and/or replace the float valve needles?

 

Are the jets clear?

 

The radiator should swing out the way to allow access to the front plugs

[Dutchy]

1 hour ago, Thumbs said:

 

 

The radiator should swing out the way to allow access to the front plugs

 It will be a tight squeeze, best ask a girlfriend with small hands....

 

I used a wooden wedge to gently "force" the radiator out of the way a bit more....

 

 

The regulator may be new, but if the altenator is on its way out.....

 

 

1 hour ago, Thumbs said:

 

 

[squirrelman]

new plugs might help.......check gap = .032"

 

post photo of all plugs in bike now. need 2 see all, not just one.

[Peka]

4 hours ago, Thumbs said:

It’s running rich .....so did you check the float height and/or replace the float valve needles?

 

Are the jets clear?

 

The radiator should swing out the way to allow access to the front plugs

Jets are clean. Didn’t check float height. 
How much should it be?

 

I can’t order air filter in country that I live.... no body have it. This is old one.

thanks for the tips regarding radiator. I’ll try once I get sparks! 

 

[Peka]

I done a little research. I should have to check floats, and float valve. Maybe they are worn out, thus it’s running rich. I’ll see that, maybe tomorrow.

 

To bad that this is happening now, when it is driving season. You should not buy bike at beginning of season, rather on end of it. That way you can do checkups and maintenance during off season. 

 

good to learn for next time.

 

 

so far, I’m really satisfied with bike, how it handles, looks, sound etc... can’t wait to fix it and to run as it should, but boy... it is hot on a but hehe...  

[squirrelman]

make sure u run a wire clear through the side holes on the emulsion tubes (main jet holders). if they're partli blocked it will cause a rich mixture.

 

btw: a compression test is a good idea when u have engine problems.

[Peka]

9 hours ago, squirrelbrains said:

make sure u run a wire clear through the side holes on the emulsion tubes (main jet holders). if they're partli blocked it will cause a rich mixture.

 

btw: a compression test is a good idea when u have engine problems.

Thanks! 

I would do compression test, but I don't have a tool for it 😞

Since I'm going to change sparks anyway, I didn't check them all. I order now and I wait till arrive so then I will change all of them 🙂

[Thumbs]

I’ve got a 1989 VFR750FK, the carbs on that are VDJOA 36mm diameter, float height on that is 9mm ....just checked that’s what yours should be too

[Dutchy]

18 hours ago, Peka said:

Jets are clean. Didn’t check float height. 
How much should it be?

 

I can’t order air filter in country that I live.... no body have it. This is old one.

thanks for the tips regarding radiator. I’ll try once I get sparks! 

 

 

 

 

 

www.Louis.eu  ships to Serbia (DHL); best order everyting in one go as shipping costs are eur 20

 

 

[Thumbs]

If you haven't already done so you should contact Joe @v4dreams.com and get yourself some Viton carb gaskets and O rings .... the originals weren't made to deal with ethanol

 

His site contains detailed photographic details about most things you're likely to encounter

[Peka]

47 minutes ago, Dutchy said:

 

 

 

 

www.Louis.eu  ships to Serbia (DHL); best order everyting in one go as shipping costs are eur 20

 

 

I will order it, just this is not related to air filter, in my humbly opinion. 
I removed air filter, just for testing purposes, and it is the same thing

[Peka]

I wanted to check if diaphrags are opening all the way and this is what I notices. One of them sometime it doesn’t close 

[Peka]

and this

[Thumbs]

I can see the slide stopping in the first video, what’s the second one showing?

 

 I washed the slides with Simple Green then rubbed the outside with a pencil to leave graphite as a lubricant 
 

 

[Peka]

9 minutes ago, Thumbs said:

I can see the slide stopping in the first video, what’s the second one showing?

 

 I washed the slides with Simple Green then rubbed the outside with a pencil to leave graphite as a lubricant 
 

 

I was thinking the same thing, some how to lubricate slides. Second is showing that only one slider opens when throttle is given. 

[squirrelman]

On 6/27/2020 at 10:45 AM, Peka said:

 

Today I’ve cleaned carbs and check membranes, they are fine. 
 

 

so u first say ok and later no ok ?  u might have screwedup cap after inspection.

 

test by blowing air into the large black hose on carbs and all slides should rise up.

[Peka]

14 hours ago, squirrelbrains said:

so u first say ok and later no ok ?  u might have screwedup cap after inspection.

 

test by blowing air into the large black hose on carbs and all slides should rise up.

Sorry for wrong information. I will inspect caps and diaphragms again... maybe I didn't put them nicely... 

[Peka]

When I blow air into black hose, only one slide rise up. I will open carbs again to check it 

[Peka]

Ok! It works so much better. Actually, is working by far better then when I purchase it. It runs all the way up to 11500 rpm. But on the end it struggles a little bit. 
tomorrow new spark plug and air filter are arriving. And I want to order new membranes and sliders. Do you know where can I do that? 
 

thanks for all help!!! 😊😊