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Carbs gone haywire!

Old 08-01-2012, 02:45 AM
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Carbs gone haywire!

Hello fellow riders.

This is going to be a rather extended post, I want to give all the details of my problem so please bear with me. Also, please take in consideration the fact that I`m not a native English speaker.

I got my VTR1000 Superhawk `97 four months ago and a month ago problems started to appear - loss of power, overheating and oscillating idle speed. Took it to the shop and found out that my thermostat was faulty and one of the exhaust valves was leaking which caused my no.2 cylinder to flood with petrol overnight.
After a compression test I found out that the rear cylinder had only 4.3psi (normal 12-13psi, europe manual). I`ve replaced the thermostat and the exhaust valve and thoroughly inspected the engine – no other problems were found. Changed the oil, oil filter, spark plugs and cylinder gasket. Compression test shown 12.8psi on both cylinders.
After thoroughly cleaning and synchronizing the carbs, I took the Hawk on a test ride. The overheating was gone, but idle speed was still oscillating and the power was nowhere near where it should be.
I measured the compression again; front cylinder 12.8, rear cylinder 6.2. Took the carbs off and measured again – 12.8 on both cylinders. After going through the posts on the forum, I decided to play with the vacuum hose, and linked the vacuum from my rear carb to my front carb. Psi reading now shows 8.9 on my rear cylinder.
I took it on the road again, and for the next 3 days, I played with the mixture and idle settings. Finally I got it close to where it should be. Yesterday, after a few rainy days, I decided to take the Hawk on the road again but it wouldn`t start. The engine turns over but it would start. Finally with allot of help from the throttle, the engine started. After warming up, idle shown 900rpm. Adjusted it back to 1250 and took it on the road.
First off, the power was gone. 2nd gear, throttle fully opened, I couldn`t get the rpm above 5000. I decided to turn back and head to the shop. Half way there, rpm suddenly spikes to 9000 and everything`s back to normal. By the time I got to shop everything was running smoothly. The mechanic took it for a ride, no problems. Ok…again, I take it for a drive. No problems for 5 or 6 k. By now the engine is hot and the fans kick into action. No worries there, since is very hot outside. I stop at a traffic light, put it in neutral and wait. Few seconds later, I hear a powerful thud from my carbs. Felt like someone was punching my ***** trough the seat. Rpm spikes to 6000rpm, engine dies. Engine starts again easily, rpm shows between 1110 and 1400, no apparent loss of power. Second stop light, same symptoms – thud, engine dies. Downhill, using engine brake I`m starting to get allot of backfire.In neutral, the rpm drops to 900 and then the engine dies. I decided to readjust the idle speed, took it back to 1250. Engine runs normally on neutral. Another few hundred meters, another thud, but this time rpm jumps to 3600 and stays there even in neutral. This is where I sopped tinkering with the settings, and took the Hawk back home. Haven`t started it since yesterday.
I`m lost here. What am I missing? The engine has only 20000k on it; the bike is in excellent condition (carbs aside).

To sum-up the symptoms:
- Massive loss of power (problem corrected itself)
- Backfire while going downhill (using engine brake)
- Explosions in carburetors (followed by engine stop or idle speed spike to 3600)
- Idle speed drops after engine warms up causing the engine to stop
- Engine won`t start without throttle help (when cold, choke on)

Carburetors thoroughly cleaned (including pilot jets) and synchronized (4 times in 1 month), fuel tank removed and properly cleaned. Fuel and vacuum lines inspected.

Last edited by Exo; 08-01-2012 at 03:05 AM.
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Old 08-01-2012, 07:02 AM
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Petcock... That's my bet... Either the diaphragm is ruptured, or you have the vacuum line on wrong...

Could be that you have other issues as well, but start by checking that the petcock flows with vacuum on the line, and stops when the vacuum is cut... And that it's on the side pointing nipple on the back, with the nipple on the bottom empty...
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Old 08-01-2012, 07:06 AM
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UPDATE:

Took the Hawk back on the road. Needed help from throttle to start, but after a few seconds, engine runs smoothly. Everything is as it should be, except that every now and then, feels like the engine is choking. The mixture is a bit lean. Due to heavy rain I was forced to take the Hawk home, before I got the chance to warm the engine. Thinking back, I realized that problems start as soon as the engine is warm enough for the fans to kick in. Forgot to mention, a few days ago, I removed the thermostat to resolve the overheating problems.
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Old 08-01-2012, 10:16 AM
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Originally Posted by Tweety View Post
Petcock... That's my bet... Either the diaphragm is ruptured, or you have the vacuum line on wrong...

Could be that you have other issues as well, but start by checking that the petcock flows with vacuum on the line, and stops when the vacuum is cut... And that it's on the side pointing nipple on the back, with the nipple on the bottom empty...
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Old 08-14-2012, 06:23 AM
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Float Valves

Originally Posted by Exo View Post
Hello fellow riders.

This is going to be a rather extended post,

I got my VTR1000 Superhawk `97 four months ago and a month ago problems started to appear - loss of power, overheating and oscillating idle speed. Took it to the shop and found out that my thermostat was faulty and one of the exhaust valves was leaking which caused my no.2 cylinder to flood with petrol overnight.


Carburetors thoroughly cleaned (including pilot jets) and synchronized (4 times in 1 month), fuel tank removed and properly cleaned. Fuel and vacuum lines inspected.
I bet the float valves weren't replaced and they were no good by 2003. They don't last longer than that, and still work well. They are some form of rubber and die like rubber. And the result is all the madness you mention. Pull the gas lines off the carbs and there won't be any gas in them, but they should be full-the gas leaked passed the float valves and into the cylinders. And while it's running they're constantly leaking, running rich and acting terrible. They cost about $15 each. The exhaust valve did not cause petrol to flood the cylinder.
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Old 08-14-2012, 08:01 AM
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Originally Posted by zxbud View Post
I bet the float valves weren't replaced and they were no good by 2003. They don't last longer than that, and still work well. They are some form of rubber and die like rubber.
??????
?????? I have no such issues from the carb floats that were used in the carbs installed Jun of 1997..


Replacing carb floats on the SH has not been shown to be a required maintenance deal as your post would indicate..

While I donít doubt someplace, sometime, somehow a float was damaged by fuel or solvent, or mechanical damage and needed replacement.. I do not see any evidence of needing replacement after every few years.

What is your basis for this suggestion.
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Old 05-07-2013, 10:09 AM
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I got here by searching for "float replacement" after suspecting the same thing zxbud is saying myself... That my floats are out of spec.

Nobody has replied to my running rich carb post, but whatever. I am using the preferred setup suggested in the sticky, and it's still giving me a bit of trouble with dialing it in. Rwhisen suggested there that my floats could be out of spec, and I believe they are. However, not too many threads on float replacement here makes me wonder... Are many of you running floats/valves that are out of apec? I mean, manual suggests half millimeters are the maximum allowable tolerance and being cheap plastic and rubber as zxbud mentions, why couldn't more people be running faulty floats without knowing it? How many people actually measure? How many of us own the $40 tool to check it? I made my own from plastic, and set the DIY tool up for the max run out according to the manual and I found mine are in need of replacing...

Just thinking out loud...
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Old 05-07-2013, 10:29 AM
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The floats are normally fine, it's the float valves that usually need to be replaced from time to time.
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Old 05-07-2013, 11:08 AM
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Meaning, the rubber seat of the valves being degraded is the reason there is greater play on the opposite end, where it contacts or is actuated by the float?
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Old 05-07-2013, 12:24 PM
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Yes the rubber tip wears and causes poor sealing
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