Overheated, cut out, now lumpy between 1-2k :(

[karl BKK]

Recently purchased a friends cherished 1992 VFR400, he loved this bike and spent lots of money taking good care of it.
He has recently changed the plugs, oil filter and oil.

After going for a spirited ride i noticed the idle of the engine had started to increase upto around 2000rpm, and while stationary i checked the water temp gauge to see it was right up in the red..... the culprit, a split main water hose.
I took it easy to get back home, but when i arrived at the next set of traffic lights the bike cut out and refused to start until it had cooled down.
I tried to ride it today down my street after fixing the water pipe and the bike is hesitant between 1-2000rpm then clears and pulls as it should do.
Any idea what the problem could be, i have checked the plugs and all 4 are sparking, i noticed that my indicators were producing a constant light (although dim) bad earth?
Or some thing more serious

Such a shame as the bike is immaculate and pulled very well across the whole rev range before hand


Thank you for any advice and i happy to find this great forum. Karl :)

[CMSMJ1]

Welcome ot the site.

Sounds like you need to check your earths for starters... Between 1 and 2k revs is on worries..mine idles at 1800 anyways!

Do you know much history on the bike? Has it eaten batteries, reg/rec or anything else since you've known it??

This is the place to be for a fix..let's have some pics in the newbies section

[karl BKK]

He did tell me and showed me the invoice for a new battery, so the old one gave up the ghost for some reason....
Am i correct in thinking that if the bike overheated too much and warped the heads, i would have irratic problems throughout the power band, not just between 1-2k
Thank you for your quick reply and i'll post some pics now :)

Karl :)

[CMSMJ1]

Doubt you've done much other than learn not to ride it with no coolant in...

batteries die as the reg rec is failing and kills them.

Seems like you had better check the charging circuit and make sure it is all tip top

[karl BKK]

Ohh there was plenty of water in the system before i went out, the bike literally burst a hose when i was out riding it.
I'll check the charging circuit, god knows where i'm going to find a multimeter here in Thailand lol :D
Again thank you for your quick reply :)

[royster81]

check your oil for mayo.......


fingerscrossed it's ok for you...

[karl BKK]

no mayo on the filler cap, i'll drain the oil when i wake up in the morning (now 3am in Thailand) :D
It hasn't used any water since bleeding and taking it for a test ride (about 4 miles) so the heads seem to be locked down true and tight.
I'm hoping it's just earths, as my revcounter was playing silly buggers before this occurred and i also noticed the indicators were emitting a constant dim light this afternoon.
Is there any thing else that could have been upset when letting the engine run hot, i have noticed a few pops and bangs from the air-box when this hesitance occurs, strange there are no symptoms of the fault after 2000rpm, seems like the bike is happy when the revs and voltages are higher?

Thanks for all the advice, it's very much appreciated, time for me to sleep and i'll read any more suggestions in the morning (hold on it already is the morning, well you know what i mean) :D


Karl :)

[karl BKK]

Well i cleaned all the earth points and alot of connections and all seemed fin untill about 15 mins of ridding and then the low rev spluttering occured again, clearing after 2000rpm.......... Regulator maybe???

[dx400r]

Had this happen to me (bust hose). These engines are pretty strong as I proved by underestimating just how much water had been lost and trying to ride another 14miles on her. Still fine tho once she had coolant and fresh oil again

Engine was still good right up until I got knocked off and the bike laid on its side the throttle jammed open. That deffo hurt her.

[Cammo]

Well i cleaned all the earth points and alot of connections and all seemed fin untill about 15 mins of ridding and then the low rev spluttering occured again, clearing after 2000rpm.......... Regulator maybe???

Well I think you've ruled out an engine issue!

It does sound like a typical electrical issue. I would be wasting your time telling you where to start.

The haynes manual has checks for the battery, reg/rec and generator. You need to do them all to tell which part is at fault.