1994 VFR pilot screw setting and fuel pump

Hello.

Some days ago I was riding my 1994 VFR 750 and I noticed a BIG sudden loss of power all through the range, just as if it was running on three cylinders, but it idles just fine.
It also started popping a little louder than it used to, since I have a very short slip-on.

I had the carbs cleaned and synced at the shop, new plugs and air filter around 3000 km ago and although it always seemed a little rough below 3000 rpm (I always thought it was because of the short slip on), the bike had good power until this day.

So I started checking everything, all parts of ignition are ok (tested with the multimeter) and I have spark on all plugs, but the plugs on the back cylinders (did not check the front ones at this time) were a little bit wet with gasoline and there was some noticeable exhaust popping only between 2500 and 3000 rpm.
I also noticed that the fuel pump is giving a 'click' every 10 seconds or so, you can even see the gasoline jumping inside the fuel filter when it clicks.

I synced the carbs myself(number 2 was way off, damn mechanic!) and set the pilot screw to 1,5 turns on all of them (that was how they were before I started)... went for a test ride, the 2500-3000 popping disappeared and the plugs are now of a nice tan color except for the one on cylinder 3 that is a little bit darker than it should, but the low power problem after 3000 rpm is still there.
I have to really rev it(much more than I used to) to go up my garage entrance which is steep.

I checked the service manual for the right setting for the pilot screws, but the one I have only has information about US 49 states, California and Canada... is the correct setting for Europe the same as one of these 3? None of these are 1,5 turns and I believe that the mechanic messed this up as he did with the carb syncing. :mad-new:
Should it be 1,5 turns because of the short slip on?

Could this be because of the fuel pump being broken, since it's giving theses clicks?

Could it be valves, even though I don't hear any strange noise from the engine and the power loss was very sudden?

Sould I check anything else?

Thanks for all your help!! :thumbsup:

 

Check scummy fuel tank, filters plugged by rust or water. No screw opening numbers are gospel, only a starting point for further tuning refinement, could be up to 1 turn more. Normal for pump to click every 10 or 15 seconds if engine is running. Suddenness hints at a fuel delivery problem but maybe electrickal too ?:sorrow:

 

This bike was parked in a garage for several years, the carbs where really dirty and clogged from what the mechanic told me, so the scummy tank causing a fuel filter plugging is very possible!

I will change the fuel filter and check it out, thanks squirrelman.

Should I use a specific VFR fuel filter or can I use a universal one?

The electrical part seems good... I tested the resistance in the coils and in the spark plug leads, the 12 plus volts on the coils, continuity on all coil wires, spark on every plug and all were within specs.

Just didn't look for vacuum problems, I will read the service manual for hints on what to check.

 

Hi there,

Yes, a new fuel filter is a good idea. I don't see the connection between plugged filter/dirty carbs and wet spark plugs, though. UNLESS, you had dirt under the float valve seats of both rear carbs - maybe. Wet plugs usually indicates ignition, but doubt if you would have either the coil or plug wire for both #1 & #3 fail at the same time. They are not wet now so let's move on. As squirrelman said, the fuel pump is acting normally. The pilot jets only really come into play at lower RPM's which fits your symptom of a little roughness and little lack of power under 3000 (trouble climbing the hill to your garage). The pilot screw initial setting for Canada is 1-7/8 turns. I have found over the years that most settings are the same for Canada and EU. So, quickly turn your pilot screws all out to 2 turns and try that before you do anything else (don't even change the fuel filter, yet, in the interests of troubleshooting - change 1 thing at a time and re-assess). If you've already changed the filter, then re-assess the symptoms before adjusting the pilot screws. Then do the pilot screws, re-analyze your symptoms and we'll move on.

Cheers,
Glenn

 

Thanks Glenn.

Today I took the fuel filter out and it seems to be full of dirt, mainly what appears to be rust that should be coming from the tank.
I'm hoping that none of this dirt passed to the carbs.

I got new plugs, new air filter and ordered a new fuel pump, fuel filter, fuel hoses (these are very dry and hardened) and will test these one by one before taking the carbs out to check.
Even if the fuel system parts I have now are still working they are all 20 years old (except for the fuel filter which is very recent), so I think it's a good idea to change them anyway.

I also noticed that the rubber caps on the vacuum connections for the carb sync are pretty hardened and slightly cracked, so I will change these also to prevent any vacuum leaks.

While waiting for everything to arrive I will check the tank for rust... any tips on how to go around cleaning it? Is there a nice effective product or is the vinager option a good choice?

 

You are on the right track. Yes, change all the rubber stuff if it is hardened. If the carb vacuum caps were leaking very badly the engine would likely be a bit slow coming back to idle after blipping the throttle. Since they are hardened, replace them anyway.

Take out the sender and petcock from the tank and try to wash out as much crap as you can with a garden hose from the top while sloshing the water around. Then you'll have a better idea how bad it is and where the rust came from (petcock, sender or tank itself). Some people use vinegar for cleaning, some diesel fuel or acetone or muriatic acid. With the acetone and muriatic acid be very careful not to get it on the paint. After cleaning with muriatic acid the metal will start to flash over with rust again almost immediately, so will need to be coated or at least fill it with gas right away. See if you can get a product called Caswell over there. If I do mine that's what I'm using. It is made to seal even with some rust left behind and incorporates that rust in the seal. Should be the easiest and most effective to use.

http://www.caswellplating.com/restoration-aids/epoxy-gas-tank-sealer.html

http://www.anvil.es

Cheers,
Glenn

 

Well, I opened the fuel filter and it was very clean and not dirty as I expected it to be... which is good, since I now know that rust is not a problem.

Got the new fuel filter in, new hoses, new plugs, new air filter but the low power is still there.
If I rev it up while stopped, it starts to backfire a lot around 5500/6000 rpm.

I also set all carbs to 2 turns, except for #3 that seems to get the plug blackened when with 2 turns, but ok with 1,5 turns.

I'm still waiting for the new fuel pump, so I'm crossing fingers before going for the carbs and valves.
Meanwhile I will check all the electric part once again.

Thanks again for your help!

 

Swap the coil and plug wire with #1 and see if the dirty plug also moves to #1.

 

Well, I'm having some bad luck with the bike...

Took the carbs out to check everything and found a mosquito inside one of the main jets!!!!!!! What are the odds????

That was that and got it sorted out, so I went for a test ride and everything seemed ok, except for a little roughness below 3000, as previously.
So I started to sync the carbs again and while doing that, for some reason the fan didn't start when it should, so the bike overheated without me noticing it (I was turning the sync screws on the oposite side of the bike) and coolant starts poring out the breather hose of the coolant reserve container.
I stopped the bike right away, pulled the radiator temperature sensor wire out and then in again, and the fan started running immediately when I turn the key on.

I now have white smoke on the exhaust and bubbles on the coolant reserve container when the bike is running... head gasket gone, right? Or could it be something else?

I never tried to replace a head gasket, but I'm willing give it my first try... is it a very complicated job on the VFR? If I follow the Haynes manual should I be OK? Do I have to mess with valves and other head parts or do the heads come out all together? Would I be better off sending it to the mechanic?

I Googled for instructions on how to do this on my VFR but didn't find anything.

Thanks again.

 

Wow, that is bad luck. HOWEVER, now that these symptoms have been identified, I think that it is the head gasket. I will also say that this head gasket was likely the cause of your sudden loss of power in your first post. It then got worse when trying to sync the carbs and started puking and smoking.

I haven't done a head gasket replacement yet. It may well be simpler with the gear driven cams, though, compared to the older chain driven cams design. I am more comfortable working with both a Haynes and a Honda factory service manual. The Haynes may be easier to follow, but confirm everything - especially torque specs - with the factory manual. It should be available here somewhere for download.

One tip from the older engines was to run the engine WITHOUT coolant until it is hot to the touch after you get it back together. This allows the bonding agent in the new head gaskets to activate and give a good proper seal. I really hope somebody with experience on this generation of engine will jump in with better advice for you.

Cheers,
Glenn

 

The only thing I could add, is don't just replace head gasket, something cause this. The head may be warped as well. Take to machine shop to check.

Kool