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Really rich mixture


oldboyracer

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After some advice before getting to carried away . 5th gen runs really rich , I had complaints from those unfortunate eneough to be behind me that they were getting stoned on the fumes. I have removed air box but at this stage left the throttle bodies in position. There is fuel inside the air box near the rear intakes and fuel on top of all 4 intake valves. Now I think it's running to cold 65c last weekend at the snowies. Could this be the problem making it run rich? Pulled the vacume line off the FPR and its dry . I don't think all the injectors could be leaking 56000 km old. Runs like a pig below 6000rpm and sounds raw not sweet. Still has lots of top end and will reach its claimed top speed just smells of fuel so I don't think it's a valve/compression blow back issue. 

 

1 change thermostat cause it's cheap 

2 change FPR while I'm there 

3 send injectors to be tested 

4 could it be one of the sensors faulty ? 

 

Hoping some  one else has had this problem and it's an easy fix (who am I kidding ?) 

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65*C is too cold and would explain running rich, mine never gets below 78*C even in winter.

But the "running like a pig below 6000" is a worry, that sounds like air or fuel problem.

Thermostat could be the culprit, Replacing it is a pain, but not too hard once you've removed TB's a few times.

I did my injectors while in there, and replaced all the hoses and O rings, didn't cost that much.

$160 to get the injectors cleaned, flowed and rebuilt, and around another $100 from memory for thermostat, O rings and short hoses.

Make sure you get the thermostat housing O ring when you buy it, you will need it.

 

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Having had a stuck open thermostat and run at that 65°C mark in cold weather myself, the bike had no performance issues. I do not think that the ECU rich warm-up mode is enough to dump the amounts of fuel that you are seeing. I could be wrong.

 

Have you ridden this bike much since you built it? Is this a brand new problem? Your description sounds like it is a new problem from the cold riding, but I thought that I would get clarification and not make assumptions.

 

If the injectors came off of a bike with a significantly dirty tank, maybe they are all in fact stuck open. (?)

 

Given that all cylinders show a problem, could there be a significant vacuum leak in the intake? If you use four gauges to tune the starter valves, are the vacuums similar to the book spec or otherwise significantly low? (Guys are there other vacuum tests?)

 

Is the fuel pump OEM, aka the pressure is not excessive?

 

If this had a cat then I would ask if that was blocked, but otherwise cannot think of airflow restrictions on the exhaust side.

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12 hours ago, oldboyracer said:

Runs like a pig below 6000rpm and sounds raw not sweet. Still has lots of top end and will reach its claimed top speed just smells of fuel so I don't think it's a valve/compression blow back issue. 

 

This part of your description makes me think you've got a Sensor Problem of some sort.  

 

If you carefully read Chapter 21 (Titled: "Technical Features") of the Honda VFR800 FI Service Manual you'll learn that the Honda PGM-FI system is pretty complex and that it uses 2 separate fueling strategies for each individual cylinder, depending on where the engine is in its demand-vs.-RPM range.  This chapter is really impressive to me because in it Honda reveals a lot of information that vehicle manufacturers usually keep hidden.

 

When the engine is operating at lower RPM and partial throttle openings the PGM-FI system uses a fueling strategy that is very dependent on Intake Air Pressure measurement (compensating the basic fueling program based on the values reported by the Manifold Absolute Pressure, the Baro Sensor, the IAT sensor and the ECT sensor).  The PGM-FI system's ECM chip contains a factory hard-coded fueling programing that was developed and optimized for a set of baseline parameters, probably including Sea Level atmospheric pressure, a "standard day" temperature and expected manifold pressures for any given RPM-Throttle Position combination (based on developmental testing of the engine).  When the VFR's engine is operating the values obtained from this basic fueling array have to be modified (compensated) on-the-fly based on inputs from the various sensors.  With the VFR's multiple sensor inputs this quickly becomes a complex and interdependent situation.

 

When the RPMs are high(er) and the throttle is open wide the air pressure behavior of the VFR's intake system becomes very hard to measure so the PGM-FI system switches to a Throttle-Position based fueling strategy (in fuel injection engineering terms: Throttle Position Sensor based fueling or Alpha-N fueling).  This high-RPM, large-throttle-position based fueling is a much simpler equation that is able to assume and/or ignore a lot of air pressure related issues.

 

The fact that you report/find that your VFR runs normally at the high end makes me think you've got some sort of sensor problem that is affecting the PGM-FI system's ability to properly compensate the Manifold Absolute Pressure based fueling strategy that it uses when the engine is at lower RPM and partial throttle opening. 

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I think at the higher revs it's just able to burn the fuel better, she was no where near as smooth and fast as I'm used to and apparently still smelt of fuel even after running at 9000 rpm for 30 mins . I think I'm going to change the fuel pressure regulator , thermostat and get the injectors cleaned and tested for leakage so that the mechanical side is taken care of first mainly because it's already apart and I don't want to do it again. Then if there is still problems I know I'm chasing sensor issues. At this stage I don't want to drop it off to the shop for diagnosis as the cost of doing the mechanicals is about equal to them pulling the tank and fairings off and having the first cup of coffee ? Will keep you informed. The issue surfaced a while ago just not as bad as it is now. The donor bike was my mates who was absolutely maticulas with its servicing and appearance (he cries now when seeing it ) I've done 20,000 km on it since putting it together. Thanks for the replies. 

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On an almost 20 year old bike changing the thermostat won't be wasted time, especially if you are only seeing 65degF engine temps.

Are the plugs fouled?  

Bad ignition coil?

Remove and inspect plugs for wet appearance or built-up carbon.  At idle, use an IR spot thermometer to measure each cylinders pipes' temp to see if they are firing.

 

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