Fuelling or Not ?

[Greebo]

Fuelling issue or not ?

Following the re-build of my bike we had to modify the carbs by fitting much larger main jets & raise the needles to the highest point to get it fuelling & running well.

Problem is if I hold the throttle in one position in top gear & cruise at say 60mph constant I notice I bit of hesitation/jerking as though its lacking fuel, if I accelerate past this its not noticeable at all, & if I hold it at slower constant cruising speeds 40 mph it seems OK...

accelerating through the gears it does not miss a beat, its only when holding the throttle in a fixed position as mentioned above.

Any ideas guys on what this maybe  ?

[Johnwebley]

could be over rich ?


 do a plug chop at that speed,

check they are not dark and/or sooty,at least you shouldn't need to sweep the pipes clean !!

[MarkCR750]

Might be worth re-checking your float heights as well, or even taking them away from the standard setting, it's possible that you are demanding more fuel than the float bowls can supply with the standard float height setting due to the larger jets.
Going the other way , I.e too rich, if you have an air box take the filter out and see what that does on a short ride, it's going to be trial and error due to the changes you've made.

[Greebo]

Might be worth re-checking your float heights as well, or even taking them away from the standard setting, it's possible that you are demanding more fuel than the float bowls can supply with the standard float height setting due to the larger jets.
Going the other way , I.e too rich, if you have an air box take the filter out and see what that does on a short ride, it's going to be trial and error due to the changes you've made.

Hi Mark

thanks for the reply, its not running rich I have checked that a few times,iridium plugs are a good colour, no air box fitted using K&N's

I did not know the floats were adjustable, however as mentioned previously when I accelerate past this I don't get a blip at all, I can power through the gears right up to 90mph no problem no blips or hesitation [90mph is the maximum I have done to date]
the problem is when I hold the throttle steady in one position at cruising speed around 60mph. but I have to say it does seem like a fuel issue, but I would have thought if it was fuel I would also get it above this speed when its obviously demanding more fuel.

I will ask the bike builder about the floats

Any other suggestions very welcome

cheers

[MarkCR750]

If you google "setting float levels Honda chopper .com" there is an article with photos on setting float heights, as you say it's ok above 60 so maybe it's not float heights, if you hold a steady 70 and then accelerate there's no problem then ?, does it do it if you hold a steady 60 in 4th gear and then accelerate ? , I'm thinking maybe the velocity of the air going through the carbs at a steady 60 doesn't suit the K&N's and doing 60 in 4th puts you at higher revs so higher induction air speed, I've got cheapo Chinese K&N's on mine with 135 main jets and the needles set in the middle, no issues in the 10 miles to the MOT station and back but admittedly that's not a lot of testing .

[Greebo]

Hi Mark
You have got a similar set up to mine, I have 138 mains & then we had to play with the needles so we tried middle setting which did work on mine it was jerking constantly, but if I pulled out the choke while riding it was off like a rocket so we new it was lacking fuel, we then went to the next notch & it was only slightly better , so then we went for the last needle notch & bingo....this got us to where we are now.
What you have suggested in your last post makes a lot of sense,
I will give it a run today & try it at a constant 60mph in 4rth.
holding it at 60 in 5th when I get the slight missing, if I accelerate to 70 it goes past the missing & seems ok, but holding at 70mph I do still get a bit of hesitation, but again acceleration past 70 it goes really well right up to 90 no hesitation at all, obviously its much harder to hold it  constantly at higher speeds on country roads, but it dosnt miss a beat powering it through the gears.
going the other way at slower speeds ,say in 5th gear again cruising & holding it at 35 or 40 it as smooth as silk.. the problem occurs when approaching 60.

I will keep you posted

[MarkCR750]

If you have PD carbs with an accelerator pump you'll get extra fuel as you power through the gears (if you wind the throttle open quickly) so that's worth bearing in mind when you are trying to figure out what's going on during your trial and error runs.

PS I think I'm right in saying that the accelerator pump doesn't operate (or not as much) with slower throttle openings and not at all when cruising at a steady speed, somebody please correct me if I'm wrong.