Re-Jetting due to exhaust????????

[craig77]

long story short, second hand engine fitted due to CCTs failing, manual tensioners fitted now, was running fine before that problem, but cant get it running right, popping and farting when throttle off, flat spot at 7000 revs onwards had some new carbs put on, ran ok for 10mins still popping a tad then ran sh#*, about to put some fuel filters to it and re clean the jets but could this be due to needs re-jetting to match the (MTC) pipes I have fitted, I got the bike with them on, don't know if he had the carbs done to match the pipes but it ran smooth as a dolphins beak, (BUT I DONT HAVE THOSE CARBS ANYMORE) if so any recommendations? ive had the carbs stripped and cleaned etc, due to sh** in them, I thought this would cure it!! its doing my nut in.

[podman]

More than likely.. consider carbs and their internals
do wear as well too.

If its doing your head in that much, id pop those filters on and invest in some dyno time, you will know what direction your heading after that.

[fabiostar]

carbs seated ok? and tight ? and vac pipe?

[MacV2]

''flat spot at 7000 revs onwards''

Sounds like timing is out 180*

[Watty]

''flat spot at 7000 revs onwards''

Sounds like timing is out 180*

My thoughts too Mac!!

[VTRDark]

I'm not sure flat spot can literally mean that. I'd have to ask if it's pushing past the 7000 mark first or behaving like a rev limiter. if it was 180 out you would most likely notice a change before that. I'd go more with the carbs as they have both been changed and have been stripped and cleaned. There's so many variables here. Is the jetting the same and is that jetting setup for those carbs and engine combined. Whoever stripped and cleaned them, did they put the emulsion tubes back in the right way around. First check for any air leaks, as suggested are the carbs seated fully and tighten back up securely. Ran OK for 10mins suggests that something has changed. Did you run low on fuel and suck some sh1t up, is the vacuum still attached to the nipple on the petcock or has it popped off. The same if you have a front vacuum take off for carb balancing. Do all your visual checks and rule out simple things first.

[Pete.L]

And don't forget there are different main jets front and back if it's on std HONDA ones. Could they have switched them over when cleaning them by mistake?

[Steve97]

''flat spot at 7000 revs onwards''

Sounds like timing is out 180*

+1

[Stratman]

Surely the first thing to do is to take off the carbs and see what jets are in there and compare against the stock items? Whilst it may need rejetting for the cans it's not going to run as badly as you are experiencing on stock setup, so carb seating/choke cables etc first before going down other routes. No point in going to all the expense of a dyno if there is something not right at the start.

[craig77]

cheers all, I had the carbs off again the weekend,(2nd lot of carbs fitted now) made sure all the jets are the correct ones, couldn't spot any shite in them but ultrasonic cleaned the jets put them back in (making sure the front ones and back ones went in correctly, fitted fuel filters, carbs are on tighter than my ex wife, vacume pipe is on and tight etc, its a bit better on start up now, but 3rd gear throttle off and it sounds like an American school dance, bang bang bang bang and still that 7000 rev problem, I hit it and pops and farts will climb ever so slowly up wards but I mean slow. if it helps it did start this problem at 6000 revs now its 7000 few more weeks and it might be 9000 revs lol

timing is 180 out a couple of you say, wouldn't this cause issues throughout the entire rev range? I took it out a few weeks ago down the bypass and screamed it through the first few gears, didn't get out of 3rd and was hitting 120mph cant be 100% sure but I think I hit over the 7grand mark in first and it was ok but cant be 100% on that, I only noticed this problem 2 weeks ago, on the way to work.

[VTRDark]

will climb ever so slowly up wards but I mean slow.

It is starting to sound like a 180 out jobbie. Do you know if there was valve damage when the CCT's failed and if the cams where removed. Depending on how competent you are with the spanners It is very easy to rule out.

viewtopic.php?f=18&t=28208&p=259219&hil ... ut#p259219

[fabiostar]

it is starting to sound like 180 out. iv just been there lol.. oh and last resort unlikely but your cdi could be fooked.as i also found out.

[tony.mon]

180 out.
Check this before messing with jetting, or when you finally give in and sort the timing you will have boogered up the carb settings.

If it turns out not to be that the you can.play with jetting.

[craig77]

Ok cheers all, well got it booked in for the "dreaded" M.O.T, told the garage to inspect the rear cylinder for timing as I believe it may be 180 out, I'll let you all know what they say I'm praying to the bike gods that it is, if I strip those carbs one more b8stard time I'm gonna go even more insane, got it down to an art form now though lol

[AMCQ46]

unless the garage know the VTR engine well, they may well struggle with what is meant by 180deg out... as all the timing marks will still line up.

they have to take the cam covers off both front and rear to work out if the cylinders are on compression or the top of the exhaust stroke to make sense of the problem