2007 vfr 800 vtec - cold start not working.

I am currently running throttle bodies that have been port matched to 38mm 2002 Yamaha R6 velocity stacks. They are of the staggered arrangement like the VFR's velocity stacks, just overall a few mm's shorter and wider than the factory VFR's velocity stacks, for increased top end horsepower.

This didn't hurt off idle throttle response that much, but added considerable mid range and top end.

Any bottom end torque and throttle response that I may have lost, was more than made up for with added ignition advance.
Unless you plan on custom mapping the front pair of cylinders separately from the rear pair of cylinders, you need to stick with the standard long/short arrangement, as the front cylinders and rear cylinders will have different fueling needs...

Any ways, why are we having a stack debate in the middle of a starter valve/wax unit thread???


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We are not, well yet, we are trading info as the conversation moves around that section of the bike.
We could do a full thread jack and add another oil debate?

 

Lol


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Tried the bike again this morning. Its still playing games but not as bad as before. Starts fine. Idles at 1500 then drops to 1200 after 10secs then gradually comes up to 2000. Once warm drops to 1300

The slight improvement is that before the revs would drop to 1000, on the verge of stalling. Alsorts of horrible mechanical noises would emit.

Since then I've had it apart again and given the fast idle another part turn. Started fine and revs dropped to normal once warm. I guess the danger is over adjusting the fast idle to the point where the fast idle jets never completely close.

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I would imagine that syncing the starter valves would help as well.


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Yep that was on my mind too. After a week I can't say things are any better.

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Your injectors may need cleaning as well.


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If you have a bore scope, check if you have a injector that does not have a proper spray pattern. It should look like an even mist. Anything eles and its a dirty/clogged injector. I had one and it took forever to prove it to the dealer. But I got video from a scope and they handed over a new injector (warranty issue). Besides, its hard to see down the bores, thats why I used a scope.

 

I've just put some Redex in the tank whilst filling up this morning. Its had some good write ups and its cheap enough. Can't do any harm and might do some good.

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I use seafoam. Its very good at cleaning injectors, safe for all fuel systems and the respected parts, doesnt leave a residue and if you add too much it wont bog the engine or strip the lubrication out of the gas. I havent used it in my bike oil yet, I dont know if it will harm the clutch or not, but I use it in my genesis coupe, both fuel and engine oil.
The fuel here is about the equivalent of burnable water. Not very good for high performance engines. So a bottle does 75l (about 75 quarts) your bike tank is about 25l so you get 3 services for you 12$.
As an oil additive, about 500kms (300miles ish) before my oil change I add half a can. Then when I do the oil change the sludge comes out and I dont have as much carbon deposits in the engine. Again this was confirmed with my handy bore scope across oil changes. My car is turbo'd so the oil goes through a beating.

 

Slight update. I was playing again yesterday. I notice that the bike always behaves perfectly when the airbox is removed. So could it be the air flow. The air filter is looking a bit filthy but not due for change for another 3k miles. Time to buy a K&N methinks.

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Check your vacuum lines, MAP Sensor and Intake Air Temperature Sensor.


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Yes, I was thinking along those lines too. This is going to be a process of elimination.

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Most importantly is the coolant temperature sensor. Not necessarily the one that goes to the temperature gauge, but maybe the one that goes to the ecu. If the ecu isn't reading at least 150* F, vtec will not engage.


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Make sure the intake temp probe is clean. If it has crap on it it will mis-read and cause issues. Also, filters dont last in terms of milage or time. They should be checked and replaced (or cleaned and reoiled if a k&n) when you start to see fuel milage drop. So if you go 130miles to a tank normally and now are getting 120 ish then check filter.

 

Thanks guys. Fuel mileage is pretty good. No drop off noticed. VTEC is engaging fine too. The filter is looking grubby but I've seen far worse. I'll have a closer look at the air temp sensor.

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Vtec on my bike engages as soon as the oil pressure comes up.
So I can not agree with your statement. Then again I have an 07 vfr so maybe the programming is different.

 

Lol are you serious? It's right there in the service manual. You should get that fixed and stop cold reving your bike over 6400 RPMs


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Jota,

Did you ever make some type of determination of this issue? I believe I am suffering from the same concern.

History: This winter I tore the bike down to do some refreshing. Before I took it apart, it ran fine. I replaced the clutch plates, changed the oil/filter, changed the coolant, and checked valve clearance (didn't have to make any adjustments). I then synced the starter valve.

So far this year my issue is mostly as was described already. I crank the bike and the bike starts at ~1200rpm. It almost immediately drops down to the point that it seems if you don't have the throttle cracked open, it will stall. If you hold the throttle open to maintain 1200rpm, it will slowly require less throttle, until eventually it maintains on its own (maybe 15 seconds). Then the idle will ramp up to a proper cold start idle speed (2200-2400rpm) and slowly ramp back down as it warms up, assuming a steady 1400rpm by the time the bike is 145F or so.

Last winter, before the tear down, when the bike would crank it would more or less jump right up to the high ideal speed (depending on temperature, 2400-3000rpm if it was very cold).

So, it seems like I am experiencing the same problem. I dug back in and double checked my work and resynced the starter valve just to make sure I didn't mess that up (My manometer had a bad seal that I found after the first sync). I can't find the problem!

Any advice?

Brian

 

I'm still fiddling is the short answer. I've come to the conclusion that the wax unit is sticking. I found that the engine would misbehave from cold every time. But if flicked the linkage between the banks of starter jets the engine would behave properly. I'm not rushing out to buy a new wax unit as they are a bit pricy, meantime I'm experimenting with penetrating oil just to remove any stiction.

My problems started in that autumn as the weather got colder. Firstly intermittent and now constant.

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