VF1000R Throttle Response

Okay my friends, my '86 VFkR has improved ten-fold since she came into my hands. A couple containers of carb cleaner (one SeaFoam, one YCC), new intake boots (to get rid of a vacuum leak), and a couple hundred miles of riding have the bike very close. She starts instantly cold or warm, has huge gobs of power everywhere; but there is one niggling glitch that I know can be corrected with advice from you experts and some time...

There is what I will call a 'hesitation' just off idle. If I don't handle the throttle just right she'll actually stall if I'm stopped at the time. The symptom also shows up as some jerkiness (and this is also easily controlled and/or ridden around) when cruising at a constant speed. Those with VF1000R's - in 5th gear at 55-60mph she'll 'hunt'. Speed up to 70-75 and she's fine.

The response under all other conditions feels spot on and very, very strong.

So... My understanding of these carbs suggests it might be pilot screws misadjusted; but I'm not an expert. Am I headed the right direction, or am I all f'd up? If it's the latter, kindly steer me appropriately please!

TIA.

EDIT: One more symptom - the idle is a little rough. Perhaps idle jets are still partially blocked?

 

You might be at the point where you need to pull the carbs and have a thorough cleaning / rebuild. When I bought my '86 500, it only had 600 miles on it, but had sat for 16 years with gas in the tank. The carbs were a mess and after doing pretty much what you have done, the bike ran, but they still had issues. I ended up taking them off and having my local bike shop tear them down and go through them. After that, the bike ran perfectly (and still does). Why not just run it as it is for now, then make a winter project out of it?

 

Yep, sure sounds like you need a good carb cleaning. Those in-tank fuel system cleaners will not fix something like this - you'd have to pull the carbs and get your hands dirty. It's kind of a pain but really the only way to get them completely clean. Good luck!

 

I do believe I'll ride the bike as it is for a while, as I have too many other projects ahead of it at the moment. The bike didn't sit for that long before I got it, and my experience with three previous Honda V-4's tells me she'll end up fixing herself with enough miles. If I do decide to pull the rack it won't be at least until it's time to pull all the bodywork to finish that part of the project anyway.

Thanks gents.

 

WARNING! Disclaimer I may capitalize some words of importance.


Your problem could be a lean condition (adjustable with fuel enrichment screws), but too many facts have been left out.
Does the bike have stock exhausts and intake?
Also all the carb cleaner and SeaFoam will NOT clean out a clogged idle jet.
To clean idle jets they must be physically removed and held up to the light to
see if they are clear.
The opening is only about .008 thousandths diameter.

If the engine hesitates unless you baby the throttle that could be the problem.
Does it backfire at all?

From what you say it is lean at idle.
The first 1/4 throttle is controlled ONLY by the idle jet and the pilot air screw(fuel enrichment).

Does the temp go up at idle?

 

No. The bike has a Sudco 4:1 exhaust system installed. Based solely on my 'butt dyno' it has been rejetted to suit that system. There is a K&N filter installed as well.

No noticeable backfire after the vacuum leaks were fixed.

From another source, the first place I should try is the pilot screws; but I think it's clear the problem is either there or with the idle jets.

Not noticeably, although I'll admit I haven't spent alot of time at idle after the engine is thoroughly warmed up. The bike generally runs in the lower 1/3 of the gauge.

Thanks Don.

 

Great point, one that is often overlooked. There is nothing you can put in your gas tank that will properly clean a set of carbs.

 

Guys, I appreciate all the input. I'm just going to make a couple of points in response before I go ride - or wrench.

1. I agree that carb cleaner won't help - IF the idle jet is completely clogged (ie: no flow at all); but I don't believe that to be the case. If it were, the bike would be idling on less than four cylinders - and it's not. All four do fire; but not equally. I know this because if I pull off a plug wire (*any* plug wire) while it's idling, the idle gets much worse.

2. I also agree that there's no substitute for a thorough cleaning/rebuild of the carburetors - IF the bike sat for a long time and the carbs dried out with fuel still in them (which turns that fuel into gummy varnish). In my case that didn't happen. The carbs were never completely dry. My bet is the two carbs on the right side (the 'high' side when sitting on the sidestand) have mildly obstructed idle jets - and I'm going to try the pilot screws first because I don't need to pull the carb rack to get to them.

Thanks again for the advice.

 

DISCLAIMER: I may capitalize words to emphasize the importance of what I am talking about.
I am not yelling or angry.


A better test.
Pulling off a plug wire will tell you something but at the risk of ruining the plug wire.
I do not have time for a detailed explanation right now.
But try this method below instead, and it works even better.

Just take out a DC inductive timing light and clip it on to any plug wire.
It will tell you if that cylinder is firing and if it is consistent.
So what I am saying is a Timing light does not just have to be used for timing,it can be used as a diagnostic tool.

BTW .... When idle jets get clogged it will still run.
The problem is that the clogged idle jet can get this black gooey
varnish that has to be mechanically cleaned out and a paper clip will NOT work and can damage the orifice of the jet.
Sometimes the hole can be very small. Sometimes you can use the steel string from an electric guitar to clean the jet.
If it is smaller than .009 thousandths you will have to go to a model shop and get a special set of very very small drill bits and turn them with your FINGERS to get that gooey stuff out then soak in carb cleaner to finish it off.

If you have a ultrasonic cleaner try that.

The thing I want to get across is that the carbs DO NOT need to be completely dismantled. Read that again.
Only the idle jet needs to be cleaned, and of coarse since you have them off install a NEW float needle.

The main jets are so large they almost never need mechanical cleaning.

 

If up for some light reading more info on carburetor rebuilding (including ultrasonic cleaners) can be found here:

http://www.motorcycleproject.com/motorcycle/text/new_articles_menu.html

 

Thank you very much for that valuable and useful information Invisible Cities!
It verified what I think about some of the new carbs. They ruined them.
They need motorcycle people in the design dept., not car people.

Honda put car people in the design dept.,. and now the young guys even say motorcycles have"bodies"! They only have gas tanks ,seats, and front fairings.
No "body" like a car.
And motorcyclists like to see the engine. and all the parts.

 

Glad you enjoyed the articles. Mike Nixon is a wealth of knowledge regarding motorcycle mechanics. He also offers a top notch carburetor rebuilding service for those not looking to tackle this 'in-house'.