Hitchcocks Forum

Hi all, I fairly new to Royal Enfield ownership with my secondhand 2014 reg Bullet Classic C5. My bike has been very hesitant in acceleration and struggles to get over 55 mph without fierce vibration.

A Bullet owner friend has tried it out this weekend and says the EFI unit needs setting up as the acceleration is very lumpy, and it should be a lot smoother. Also the top speed should be more than 55 mph.

I thought maybe the gearing had been changed but its all correct. Any thoughts or ideas as to where I start looking for a solution would be most welcome. For over 30 years I've always had BMW twins ands singles and thought my RE's acceleration was typical of all REs, but my mate reckons it should be a lot smoother.

Sorry that I can't come up with a solution, but I can say from my experience that there is something sadly wrong here. My EFI (when the brakes are not binding) will happily cruise at 60.

You haven't said how many miles the bike has done; they do smooth out as the mileage builds up. There are a number of things that can cause poor running. First of all check the battery leads carefully, including the small gauge one to the -ve terminal. Then check all the sensor connections, particularly the throttle position sensor. Sometimes the voltage on this needs to be reset too. Does the bike have the original exhaust and air filter? If not, does it have a Power Commander fitted? Is the spark plug a nice colour and is it an NGK BPR6ES? The original Bosch clone plug is utter rubbish. You should check the plug cap too especially the connection between the lead and the cap. Best to replace the metal cap with an NGK. These bikes do vibrate to some extent because they are a long-stroke single with no balance shaft. Mine was awful above 55mph until it had a few miles on it (1800 or so). I found that giving it a few runs at full bore in short bursts helped a lot, together with replacing the standard exhaust and header with a Hitcocks replacement. I also converted my C5 to a carb; most prefer to fit a Power Commander V if they change the exhaust for something less restrictive. I doubt there's anything seriously amiss with yours; like many of them it just needs sorting out a bit. They are not like Jap bikes ( or anything else really). Once sorted it should be smoother at higher speed but it wil need a few miles on it.

Many thanks for the replies and info. I'm checking out the items on the bike today. It's done 6800 miles, has the original hefty exhaust and everything else looks standard. I'm looking forward to getting out and about on it over the Christmas break. Merry Christmas......

It sounds like battery to me. I had the same on my 2011 C5. Even though the manual says the pd needed to operate the fuel pump is only 10.4v in practice it needs to be a very healthy 12.4v. It would start OK but runs as rough as buggery and wouldn't pull the skin off a pudding. New batt and it was as right as ninepence.

I forgot to mention that the vibration can also be reduced by slackening off all the engine bolts, running the engine, revving it a bit then stopping it and tightening the bolts to the proper torque settings. The engine mountings are often not torqued up properly and the hand-made aspects of the machine build at the factory can result in the engine not sitting as centrally as possible in the frame. Chain alignment can also cause additional vibration. FWIW I changed my original battery for a Motobatt one because I didn't want a wet battery leaking electrolyte on the frame and because the AGM type produces bigger cranking current. Also the Motobatt allows the battery leads to be fitted so that they are not under strain, as is the case with the original. I kept mine for testing electrical things on the bench. Most of the poor running on mine was down to the tps, but problems do tend to be electrical mostly. It's a shame that this forum has no provision for stickies; if it did we could list common problems with the EFI in one place...

Have a look in the news section of the home page - it has an article which relates to the problem you are having about an inner air filter cover which has been left out of most of the early C5 / B5 models which causes this fault.

Just fitted the insert to my classic EFI. It got rid of the flat spot (hesitation when opening throttle) There is a bit less top end power but still pulls @70 mph with little vibration. Engine has 2k on it from 2010. So with my limited knowledge I suspect some other issue is your cause. It is worth the little expense if you don't have one fitted in any case.

Andy McC are we talking about AIR FILTER PLASTIC COVER Part No 591681? Do you know from what year this is fitted by any chance? Thanks

Hi Nigelphoto. That is the correct part. Apparently they should be on all C5' s. If you can see the air filter on opening the cover, you need one. Mine is 2010 direct import but I think they should have been fitted from day 1 as there is no way to get proper breathing without it, unless you tape over the cover-airbox join. It completely cured the annoying flat spot which saved me a few Bob as I was going to do the carb conversion to overcome it. Think the OP has another issue though as mine still pulled 70 without it.