86 vfr700 hard to start....makes air pop sound

Advice anyone.......

I have an 86 vfr700f. Once started and warmed it throttles up smooth and pulls strong. I know they are cold natured but i think this is more than that.
The bike makes ,what I can only describe as an air suction popping noise, when it almost starts. After a few tries of turning the ignition off, then back on, pulling the choke, while keeping the throttle rolled forward(not twisting at all) eventually it starts.
I have replaced the fuel lines,filter,pump and exchanged the tank for one that does not have rust. My thoughts are that since it runs,rides and pulls good when started that it may just be 1 or 2 carbs that need rebuilding..or should i just have a complete rebuild done?
What other year vfr 700 or 750 carbs will fit my 86vfr700, I have heard that any years 86 - 93 are the same?

Thanks in advance for any advice

 

Look at your choke cable adjustment...make sure the plungers are completely open when your choke cable is pulled max.

If it's been run with a rusty tank it almost always finds its way into the carbs. If it's only rust it usually comes out easy. A complete rebuild maybe isn't necessary...you don't know 'til you look.

Another way to tell if the choke is working...warm up your bike and apply full cable while idling. It should make your bike pretty near if not stall.

 

Carbimatators

Has the bike sat for a period of time unused?

 

Yes it sat for awhile,:frown: 6 months that I know of.....:frown:

 

SO throw in some chemical fuel system cleaner like SeaFoam.....

ALSO get rid of any OLD fuel and possible water in the tank by draining it completely. Drain carbs through bottom screws.

New sparkplugs always help starting.

 

sitting

This is a bit of a pain if you have not done it before but it is not to tough. Pull lowers and the tank and side panels. Pull the air box and cables, choke is easy but the throttle is a little trickier. Loosen yuour boot clamps and pull the carbs out and flip them over and pull the bowls. Remove the jets and clean them with carb cleaner , you may need to run a strand of wire through them and look through each one at a light to be sure they are clear. You may want to wash the rest of the bodies down and spray cleaner through ports or compressed air. If you pull the slides do not get chemicals on the diaphrams as they may swell. Put jets back in and swap the bowls around so the locks for the air fuel mixture screws are on the oposite side. Now you can adjust them when you want.Install carbs and tank. You will want to drain the fuel so jump the fuel pump with a couple of wires, one to bat ground and one to bat hot and pump it all out . If you have fresh gas in it already you will still need to jump the pump to charge the system or you will crank on it till the cows come home. let the pump run till it stalls and it should fire right up.

 

Based on the problems I've seen people, like new mechanics, have with it, I would say it can be really tough. And as these bikes get older more and different problems show up. I've seen carbs broken from being pryed out of boots, jets turned around, diaphragms tore and out of place, and the ever popular "slow jet still clogged" after all is back together, not to mention broken float towers from sticky pins and "now where did this hose go?". If you're a newbie or careless...they'll likely be off at least twice before its right. So...don't underestimate how quickly your repair can turn into a $#^@ up.

If you decide to tackle it, there's a good 'how to' on a website belonging to a guy that hangs out here once in awhile...Jamie Dougherty. I've read through it and it's pretty good. One thing you may want to pay particular attention to that doesn't always get mentioned (since it could relate directly to your problem) is the enrichener jets. Each carb has one, often right next to the main and slow jets...sometimes in a long brass tube in a separate chamber of the float bowl, but almost always fixed...so ya can't take 'em out. Make sure they're open. If clogged your enrichener won't get fed fuel on that carb...making your bike start hard.

 

SO, in other words, do the easy stuff that a noob can't screw up first, like SeaFoam, drain the tank, and new plugs??