Hitchcocks Forum

Hi all,

2007 G5 bullet EFI

I know this is probably something obvious, but need to ask. When I first start riding about one minute in, my bike starts backfiring with loud pops and hesitation. Like riding a bucking bronco. Very embarrassing. After it warms up at high revs for about two minutes it stops and runs fine. I try to fix everything myself, but the mechanic at the local dealer mentioned something about an automatic choke for the first few minutes and I am wondering it is making it run too rich and fouling up my plug.

Thank you for any advice.

If it is similar to the "choke" on my C5 you have to hold it on, so unless there's no slack in the cable or the cable is sticking I doubt that that is the issue. It is not a choke as such anyway; it opens an additional airway in the throttle body, resulting in the ECU enrichening the fuel supply. The more usual problem is that the cable is too slack so the airway cannot be opened properly, which is why our host sells a cable with an adjuster in it. FWIW I never use mine, I just open the throttle a little. You don't say whether or not your MIL comes on, indicating a fault. If it does then you need to establish what fault code you are getting. FWIW my C5 a while ago would start ok then stutter as I opened her up once off the estate and onto the main road. This disappeared once the engine was warm and I out it down to the weather becoming colder. However, it gradually got worse until the engine would be difficult to start and the lurched and stalled to such an extent that the bike became unbridgeable. It turned out to be the throttle position sensor connection. This had not fully clicked into place from new. Eventually the connection failed completely caused my the engine to flood. I did get a MIL light at this stage, but not before when it misbehaved only until it warmed up. If I were you I would check the tps connector and the infamous negative battery connector; in fact it would be best to check all the sensor connectors, assuming that there is slack in the "choke" cable and that it hasn't stuck on. Good luck.

Popping on the over-run can be an air-leak on the exhaust, probably at the head. That can also cause some hesitation on pickup from closed throttle but not kangaroo clutch syndrome, more flat spot and - wait for it, wait for it, omg! wheelie! When it warms up metal expands and shuts the leak off. These bikes shake and need bolts tightening as a routine; I tighten the exhaust flange with a nut driver when it's hot, there's a compression washer in there, so not the big socket wrench then. There's a torque setting no doubt but it's until you cannot twist the pipe with moderate force. Loctite won't work here, the heat burns it off, the ideal solution is long brass or copper nuts.



Yes it could equally be the electrics, for much the same reason. The plugs 'n sockets do shake apart but they also corrode, pulling them apart and putting them together again scrapes the oxide layer off.

That choke thing, the oddly named 'bistarter' is a weird thing. The cable lifts a plunger on a valve to the top of its travel and must drop it back to the bottom again. On mine the cable does flat nothing at all until 50% of its travel, then it lifts it right to the top. Hence there's a lot of slack when it's down. I only use it on cold mornings and then it will start first kick or it's close the bistarter and give it full throttle on the electric wellie, it may need me to then hold the bistarter on for 30 seconds until it will idle and then give it a few minutes to warm up (lid, gloves, zips, gate).

I've had popping issues ever since I've had this bike, a partial solution has been to increase the idle speed for smoother running but the exhaust flange does loosen itself.

My cable is the same. Now that the engine has loosened up a lot I usually kick start it. I find that doing this while holding open the bi-starter is just plain awkward, which is why I now just open the throttle a touch, keeping it open for a while as necessary. I should perhaps mention that I have removed the side stand cutoff switch on mine. I don't care for kick starting any bike on its main stand and find it easier to start standing beside it - usually first kick now, but a PITA until the engine loosened. I can now leave it ticking over while I put on my gloves. Also, it's one less connection to play up.

Torque for engine exhaust studs on the EFI is 14lbs ft., do it COLD, not hot. Make sure you have the correct gasket - there are two types and the one shown in the w/s manual which you order is bound to be the wrong one (one's round and is supposed to be for the 535 but it fits my 2011 C5 and the other is flat). Popping and banging on the overrun is normal certainly for the C5 although not the 'bucking bronco' and the hesitation. EFI on a big single is notoriously difficult to fuel correctly and the old fashioned Keihin used by RE is fairly basic but it does work if you can put up with one or two 'characteristics'! As Rattlebattle said - check the MILand the sensors.

Designing big singles even with a carb isn't easy, apparently. I've just started re-reading my old seventies onwards Motorcycle Sports mags and come across an article about the development of the Yamaha XT500. It seems they had all sorts of issues trying to get the engine to run without self-destructing....
FWIW my C5 hardy ever pops or bangs on the overrun. This could be because 1. I have the factory set (high) tickover and (2) I have the original exhaust etc. Personally I don't like popping and banging. I don't accept it as normal. It usually signifies something needs adjusting especially on a bike with hardly any valve overlap.

The plug was fouled - bingo!

Well then - after the last post I went out on the bike and had almost but not quite exactly the same problem: pops, bangs and misfires.

I knew I was low on fuel so headed for BP Ultimate. It does misbehave when running out. Does the ECU go into limp mode? However the low-fuel was not lit (but last time this happened the low-fuel bulb had blown). So filled up and had a nice chat with a copper admiring the bike. Coming back most of the naughties were disappearing but not quite gone.

So I pulled the plug.

Et viola, the plug was fouled with black soot although the electrode was clean grey.

Best guess is bike hasn't been run much for last two weeks but has sat idling several times.

Clean up and refit the iridium NGK and all is well.



Rattlebattle - I always kick on the centre stand from old habit. Pull bars to left, grab the left bar to steady myself and thumb the bistarter then give it a prod whilst standing on the right. If the bike is off the stand then I straddle it, I seem to remember having dropped a bike standing with it unsupported; on the side stand the kick goes down at a funny angle for me. Having started I leave it idling to warm up, which is probably how it's got sooty plug and exhaust (I'm thinking Redex and italian tune up). If I don't use the bistarter she won't start from cold on the kick.

A big kick is useless, if she won't start after a few prods then it's 3 seconds on the electric wellie; usually starts first time, prolly floods cos the ECU does prime the injector for starting.

I may disconnect the side stand switch, I've never made a habit of leaving it down but it is easy to come off the centre stand with the side stand down and forget it is lowered; that has caught me out with a, "won't start" a few times.


The plug was fouled.

The thing about these bikes is that they're all a bit individual. I choose not to use the main stand because I've seen too many distorted by applying forces to them that they were not designed to take. For me, the kickstart seems odd compared to the many other bikes I've owned over the years; it is angled whereas most are straight. For me, it is easier to start it standing by the side than straddling it, though it's the only bike I've done this on. The fuelling on the EFI reminds me a bit of the LE Jetronic system fitted to the two early K series BMW bricks I once had. I couldn't blip the throttle on those either because there was always a flat spot, like having a cutaway that was too large. Also, I could get them to bang in the exhaust at will. On a closed throttle the fuelling was cut off. If after a fastish run you closed the throttle and then opened it just a fraction you would get a seriously loud explosion a unburnt petrol ignited in the silencer. Like the later oilheads unused fuel was returned to the tank. I think the RE EFI system doesn't do this ie it only supplies fuel according to need. Does anyone know if this is true and whether or not the fuel supply is shut off on a closed throttle but when the engine is revving above tickover speed? It seems to me that not an awful lot is known about this system; certainly a lot less than the Motronic system on later BMWs or the system on Triumphs with EFI.

I think the main thing for Brucehur is that having acquired the same 'fault' on mine is that running it on the bistarter/choke which will indeed make the mix rich, does foul the plug up in short order. Something to keep an eye on. First job then is pull the plug.