VFR Power Loss/Non Responsive

Evening all,

Been a while since I posted and looking for some help (again).

Riding home from work today along the M62 - noticed significant intermittent power loss on my VFR (1998 incteceptor).

Basically when cruising along at 75-80, even with the throttle fully open I was loosing speed in 6th and 5th gear. The bike was slowing down, then she would "jump" back into life. When I hit quieter roads, pulling away from traffic lights was not fun; even in lower gears there was just no power there at all (very slow to accelerate), then all of a sudden bike would jump back into life.

Bike is now 27 years old - I don't want to lose it as I really do like it but I also don't want to put stupid amounts of money into fixing it. Could someone with a bit of knowledge sense check my below check list to see if this makes sense:

1 - Service time (oil/filters/sparkplugs)
2 - If this makes no difference, valve clearances
3 - If valves all ok, compression check
4 - If all ok at this point - kick something really hard and swear a lot, probably whilst jumping up and down

 

If it was running OK but then started giving issues then I doubt that changing oil, filters or plugs will magically fix a fault but also will do no harm. A blocking air filter or worn plug will cause a progressively worse problem not a sudden onset like you are reporting.

I'll go out on a limb and say it sounds like a fuel supply problem. How full was the tank when this was happening, a failing fuel pump often gets worse when the level is low as there is less cooling from fuel. Maybe also water in your fuel, or a blocked tank vent. Do you park the bike outside at work and was it raining a lot? A blocked filler overflow pipe can cause rain to enter the tnak.

 

my SV650 was having a similar problem for a while, turns out one cylinder was intermittently going dead because water had seeped into the spark plug well and was shorting out the spark plug. it sounds to me like you're in the same boat, since when the fault is happening it's down on power but still able to move, and power comes back right away when it decides to work again. if it idles rougher and the exhaust note changes when it happens, or if you smell fuel, then that's almost certainly what's going on.

first thing to do would definitely be a fresh set of plugs; when you pull out the old ones, check for:
-wet or excessively dirty: no spark, possibly bad coil or plug boot
-discolored or burned: no fuel, possibly bad injector
-excessively worn: was just time for new ones

 

Thanks Terry - Bike is dry stored at all times (garage at home, underground car park at work - no rain today) - had a full tank before I left for work this morning - half tank on way home. Will check the lines at the weekend when get a chance to start pulling things apart

 

Thanks Burger - will pull the plugs at the weekend (and check the vaccum lines as well as Terry suggested) and see if that improves things - i remember having a similar issue on a Thunderace a few years back and it was the plugs misfiring

 

@Burger @Terry Smith - just to update on this:

I have pulled the plugs under the fuel tank and had a look at them - there are some oil traces on the plugs but not sure if this is enough to be concerned about - ive not had time to pull the plugs behind the oil cooler yet (hopefully tomorrow)

Checked the air filter - all looks ok to me - there was some very slight oil "misting" in the filter housing but I believe (please correct if wrong) that this is not something to be concerned about.

I have uploaded a picture of the pulled plugs below - I have tried to upload a video of the rev counter at idle but not been able to do so on here - effectivley the bike sits at 1500 RPM, then jumps intermintantly to around 2.2 then back to 1.5

Tomorrow (if I have the time) I will swop out all of the plugs, let the bike get up to temprature and see if the problem repeats with the spiking

 

rpm jumping is elektrikal. check wires and boots for cracks in insulation. what gap on plugs ? what # are the plugs ?

 

Had some free time today and managed to get stuck into it - pulled all of the plugs and carried out a compression test and a leak down test - no issues on either.

Cleaned out the HT leads, went through the vaccum hoses with a can of compressed air and put the new plugs in. Bike runs like a dream. Starts instantly, sounds much better at idle and no intermittent jumps. Let the bike sit for 30 mins with the engine on to warm it up then took it for a spin - no problems to report with loss of power etc - hoping this was a faulty plug or a bit of a blockage somewhere which I have managed to clear

Bike back in my garage - whilst the fairing is off going to bleed the coolant (not been done in a long time) and do an oil and filter change - hopefully all set for some decent weather riding

Thanks all for your suggestions much appreciated (as always)

 

nice job, ya fixedit.

for best coolant change, dont forget the cylinder drain bolt on front of engine behind the headers.