Honda VF1000R engine tuning

I have a VF1000R engine with stock type restrictive mufflers.
The intake is foam free breathing and No rat maze. just direct.

I have 128 main jets and #40 idle jets. OK I could go up to 150 mains and get some real top end out of it.
After all the 49 state models used #145 mains...right
But I do not want what little gas I have to get used up in a quarter mile.

So the main consideration is the midrange which is a little lean.

I put four small brass washers under the needles which I got at a hardware store.
They had to be filed or sanded because they had rough edges. That makes them about .022 thickness.
The washer has to be small and fit into that little depression in the bottom of the slide.
Then you will have no trouble putting in the little plastic keeper with spring.

On a regular needle that has 5 grooves and a clip (tunable) The space between grooves (if I remember right is about .050
so a .022 washer is not much effect.

So I installed the washers and started it up . No problem on start up , and excellent throttle response with this slightly richer mixture.
I will report back on spark plug color before and after the washers.

REPORTING BACK...The plug color is a light tan with outside rim slightly darker - perfect.
Before the insulator was almost white and my fuel /air meter I had on temporarily said the mixture was lean in the midrange and idle. I turned out the mixture screws 1/4 turn and got a dramatic improvement in throttle response and better plug color. Cold starting at the beginning of the day was better too. Did not need any choke at 75º temp.

 

Donald, What did your air/fuel monitoring tell you? I'm running 130 mains and 40 idle jets and I'm getting a carb backfire, indicating a lean condition I believe. I just bumped the jets up from the original 122/38 but it hasn't helped and the bike seems to be running very hot. Dynojet's stage 1 kit comes with 136 and 150 mains. The bike has aftermarket Kerker exhaust and a K&N air filter. I'm thinking I need to bump the jet sizes up more. Any thoughts?

 

The fuel /air monitor kept showing LEAN from idle and all through mid range.
So I added 1/4 turn air pilot screws, and shims on the needles, and it significantly helped.
You are on the right track. The engine will accept 150 mains but the mains are only a small part of the whole throttle range.
I basically have the same set up.
You did not mention the pilot air screw.
I would start with 2.5 turns out ,on the pilot air screws.
Any backfiring is usually a lean condition. The needles control midrange.
The midrange is not being addressed. Try the shims on the needles. They are easy to get to.
Try one brass washer under each needle.
It helped mine not be so lean in the midrange and Factory Pro told me their kit includes a needle with the standard 5 grooves.
So just the fact that their kit includes needles with grooves means that they must know the midrange needs to be fattened up.
I probably will go to 130 mains too. I have 128's now.

Look at the plugs after EACH change.
Only make ONE change at a time.
Look how much of the throttle is controlled by the needle and clip position.
Also when I added the shim under the needles the radiator fan did not come on in 80º stop and go traffic. IT must be running a little cooler.

 

Will do, thanks. I think I'm 2.5 turns out now on the pilot screws. I'm thinking the needle washers will be my next step and maybe 140 mains, but maybe bumping the idle jet size up too. The bike is idling when I shut it off and on restart it backfires so I'm suspecting the idle jets as the main cause. Pulling the plugs each time is a PIA but I guess it needs to be done...they've looked ok the few times I've pulled them. <sigh> My fan temp sensor is bad, I've got the fans tied in to a toggle switch and just turn them on as soon as the temp gauge gets to about 1/3.

The backfire tonight blew out one of the 1/2 moons on the rear valve cover gasket, about 3 miles from home. It spat oil all the way home - me, the bike, the exhaust..quite a mess to clean up, maybe I should call BP???

 

Wow- blew out a valve cover seal !
If it is hard to start you might want to go back to that #38 slow jet.
With my #40 I have to not give it too much choke especially in this hot weather.
Since you have the STOCK air box with foam filter it is much more restrictive than what I have.
I have cut off the stock air box and just have a flat foam filter over the inlet screen.

When pulling the plugs you only have to pull one plug -not all of them
You would only pull ALL of them if you were troubleshooting some kind of carb problem.
Just go back to the #38 slow jets, and turn out the air pilot screws another 1/4 turn.
I know it is a pain in the ass but the reward is worthwhile.

By the way did you put a lot of oil on the foam filter?

One more thing....The VF1000F shop manual shows #140 &145's for the 49 state model in the shop manual for the stock bike. Same engine-same carb.
My air filter below.

 

It isn't hard to start, starts up pretty quickly. It's when it's hot I'm having the problem on restart. Filter was oiled pretty typically, not too heavy.

The VF1000F manual I have lists 150 front mains, 145 rear, I assume that's 49-state. 138/135 for the CA model. But I get your point, they are basically the same motor.

 

Yes you are right. I should be more precise with that info.150-145's
My bike has #128's and it pulls hard when wide open.
My speedo only goes up to 140mph but it is still pulling hard all the way !!!

I have some good info for, you but I need to send you a private email.

 

Let me say something about the backfiring.
When it is idling and you give it throttle and it wants to bog or stall, and back fires that is one condition,
But with a #40 idle jet it may be back firing on start up by all the unburned gas still in the header pipe etc.,.
Remember you can turn the pilot air screw out 3.5 turns if needed. Then think about a bigger jet.

 

This afternoon I put in the 2nd shim under the slide needles.
I had to shave the little protrusion down in the plastic keeper about the thickness of one shim.
I used a #11 Exacto blade.

I pushed the spring back onto the post with the tip of the Exacto blade near the base of the spring.

The result was good on start up partially warm from riding a couple hours before.

This time when revving the engine there is NO hesitation no matter how fast or hard I twist the throttle.

Next is the road test to make sure it does not backfire from too much unburnt fuel in the exhaust system,and
if there is I can probably just turn the pilot air screw back in 1/4 turn.

 

I just test rode the bike and it is much better!! Pulls hard and no backfiring from unburnt fuel on decelleration.
So two washers it is.!!!

 

Hello Mr. Branscom,

How about an opinion on this carburation problem. I have a totally stock 1985 VF1000R. Carbs are stock, just rebuilt by Billy Carr. I balanced the carbs and ran the bike for an afternoon. Runs strong. Went through 6 gallons of gas in 88 miles. That's 14.5 MPG. ouch.

I am not a carburetor guru. What could cause such lousy mileage, gas fumes out the exhaust, yet the bike seems to run okay?

Thanks for any opinions,
Kevin Savage

 

You say it runs good but 14.5 miles for 6 gallons !! WOW.
Is raw gas coming out of the exhausts? .....If NOT then
Does it have the stock intake parts???
I am wondering because I think the reason is that some gas is being sucked out through the float bowl vents.
Is it a 49 state model???? If so check and make sure that little metal plate is over the vent tube inside of the plenum area. The rubber tube cannot be left open to wind rushing by it because it will suck gas right out of the float bowls.


Also when you say you balanced it , do you mean synched the throttle shafts????

 

Hello Mr. Branscom,

yes, there is raw gas spewing as a heavy fog from the mufflers. The bike is a 1985 49 state model VF1000R. The Carb intake system is intact and correct (aluminum airbox, rubber venturis, air cleaner box, Honda paper air cleaner). The carburetor rubber insulators (that seal the carbs to the engine intakes) are new. The float needles and seats are new, just replaced at the Honda dealer in Las Vegas. Two Honda service mechanics at the local dealer have inspected the carbs and state that the needles and jets are stock-sized but, not Honda original parts. Billy Carr put in the needles and jets as part of the recent carb rebuild he did for me.

I synched the carbs using a new Morgan Carbtune I bought from the Morgan folks in Belfast.

any opinions would be most welcome...
Sincerely,
Kevin Savage

 

OK...Here is the next step..
When the engine is cold remove the spark plugs and look to see if they are all covered in black soot or look normal and light brown.

If the plugs look normal (doubtful) then I think something is causing a lot of gas to go down the intake system. Make sure the vent hose/hoses DO go to the right place.

I would pull one of the slides out and look at the needle. Does it have grooves with a circlip or does it have no grooves? If it does have grooves and a clip tell me WHICH position the clip is on.

ALSO check the float bowl vent tube.
It comes from the carbs and goes into that aluminum plenum chamber.
Inside the plenum chamber where the hose comes through there should be a metal clip over the end of the float bowl vent tube. It covers the hose but does not block it off. If there is nothing over the vent tube then that is the problem. I think the clip is held on by one or two screws. If you remove that clip make sure you put Locktite on the screws and let sit over night or else a screw could get loose and get sucked through one of the intakes! The gas is getting sucked out of the vent(float bowls) and directly into the intakes of the carbs.

One other thought.
The sheet metal cover on the top of each carb has a little bump on it and that is a vent so pressure is vented from the area above the slide piston. The little bump is next to one of the 4 screws holding down the sheet metal cover and the bump is formed into the cover. Make sure that hole is clear and someone did not put gasket sealer over it. Just a thought.

 

Hello Mr. Branscom,

I will check the items you suggest. I do not know what you mean by...

Maybe I do not know what I am to be looking for. I have included the photos of the completed carb assembly. The aluminum plenum chamber (aka., aluminum air cleaner base?) there is no hose, nor a hole for one. Or am I looking at the wrong part?





Thanks for sharing your knowledge...
Sincerely,
Kevin Savage

 

You are looking at the right part.
Carb base pan/plenum chamber.

I do not see any place that the float bowl vent comes into that.
That raises the question ....Where does the vent tube go to???

BTW those carbs are really clean. Wish i could get them that clean. Makes me think they may be powdercoated.

 

Solving the mystery VF1000R 1985

In the photo

I do not see a vent coming into that area from the float bowls.
Not to be alarmed I have seen at least 3 different versions.

Just follow the float bowl vent tube and tell me where it goes to. Post a photo.
If it just goes to atmosphere there is supposed to be a little flap valve on the end of the hose to keep gas from getting sucked out. You can do without the little flap valve if you keep the end of the tube out of the airstream tucked away.

Could you post a TOP VIEW of the carbs? Thanks.

 

Hello Mr. Branscom,

to answer the question of the air vent tube, the carburetors vent tubes connect to one central tube that runs straight back (horiontal) from the carbs to the area just ahead of the rear shock and drops straight down between the rear shock and the fuel pump. The open end of the tube is level with the bottom of the shock spring and is open to the air.

BTW, the fuel vapor/cloud comes out the end of the mufflers when the bike is standing still, too. Not just when there is a good airflow over the bike.

I am taking the bike back to the Honda dealer once I return from Xmas holiday. I will be out of town until the 27th. The dealer said it could be a mixture problem (a mixture problem wastes 30 mpg?. I only get 14.5 mpg now). I will post the extra photos yiu wanted and an update when I return from holiday. Wishing all who read this thread a Merry Christmas.

Sincerly,
Kevin Savage

 

Hello Mr. Branscom,

here is a photo from Honda. Item #1 is the fuel line into the carburetor block, #2 is the carb air vent running back (out of the picture) to an area above the rear shock.




Sincerely,
Kevin Savage

 

The Dealer said it could be a mixture problem. But you told me the carbs had been rebuilt completely.

That vent tube needs to be tucked away OUT of the air stream. Do not block it off though or the carbs will not get any fuel.

If you are taking it to the dealer why spend time on the forum to get answers?
I am a ex Honda mechanic and I do not like to waste my time if you are just going to take it to a dealer anyway.