VFR750 engine won’t rev

[Farmingstock]

I’ve recently bought a buggy with a VFR750 engine that’s been fitted then left to finish off.

I have managed to get the engine started, more by luck than good judgment, but only by pouring fuel down the pipe that was connected to the fuel pump.

Before I throw any money at it I wanted to make sure the engine was sound and revved up at least.

Atm it starts on the button but even with the throttle fully open it won’t Rev up just stays around tickover.

I’m not using the fuel pump atm and I’m not sure if the correct wires are on the correct coils if that makes any difference?

I know all 4 plugs are sparking but not sure if they are in the right order?

The fuel in my temp tank feeding the carbs doesn’t disappear fast it’s almost like nothing is being used so not sure if it needs to be forced by the pump? I put the pump in some fuel but although it was working it wasn’t sucking so maybe needs priming?

Also does it matter which coil wires go to which coil? I’m pretty sure they are right as it starts fine but could there be another reason why it starts fine but won’t Rev?

[stinkwheel]

Well, check it's running on all four first of all. Spot of oil on the headers and see if they burn off at the same time.

Do you have the airbox on? If not, you will probably need it.

If it's like my two VFR750's (3rd and 4th gen) the pump shouldn't be sat in fuel, it's an inline pump that's normally attached to the subframe. The pump is gravity fed from the tank then lifts the fuel to the carbs. It has points on it which spark, putting it anywhere near an open source of fuel is a recipe for a large fire. If you've put it in fuel, you'll need to strip it, clean out the fuel and clean the points with contact cleaner.

Mine runs badly and cuts out if the pump is playing up. that said, I'm not sure if fuel flows without the pump working. I'd expect gravity feed to work at least somewhat, it's not a particularly high pressure pump, more a lift pump because part of the tank is below the level of the carbs..

Of course it matters which order the coil wires are in. There are different firing orders and ignition systems on different models of VFR750. Some have a wasted spark and two pickups on the crank, some have a single spark and have pickups on both the crank and cam. I think you need a workshop manual!
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Farmingstock]

Hi, thanks for the reply, it has the air box etc but as you can imagine I have a box of parts and it’s a guessing game, I thought I did ok getting it started but yeah the next step is getting it To Rev.

I will try again with the coil wires, it’s more the correct firing order, could do with a wiring diagram to check which goes on which cylinder.

Will clean the pump and try priming it to see if it pumps, was only at it 20 minutes and as it’s in a buggy the wires don’t reach properly and the tank isn’t on it! Just a temp thing just to get it working with what I had before I got fabricating.

Will keep searching for a manual, but should be fun once it’s moving!

[ThatDippyTwat]

[Farmingstock]

Great thanks, I’m not sure on the year, will try and find the engine number next time I’m there, where about on the engine is the number? It’s been bolted to the buggy so some of the engine is hidden but I’m sure I’ll be able to find it.

[ThatDippyTwat]

[Farmingstock]

Hi, thanks for the reply, it has the air box etc but as you can imagine I have a box of parts and it’s a guessing game, I thought I did ok getting it started but yeah the next step is getting it To Rev.

I will try again with the coil wires, it’s more the correct firing order, could do with a wiring diagram to check which goes on which cylinder.

Will clean the pump and try priming it to see if it pumps, was only at it 20 minutes and as it’s in a buggy the wires don’t reach properly and the tank isn’t on it! Just a temp thing just to get it working with what I had before I got fabricating.

Will keep searching for a manual, but should be fun once it’s moving!