Bonneville America Forums Forums Technical Forums Performance Mods New Tank and Fuel/Oxygen Starvation?

So, got the tank done and had a aircraft style fuel cap put onto it. Bloke who did it mentioned that it might affect performance and said to drill a couple of holes under the tab

(realised my description isn't up to much so picture of the cap is - http://www.merlinmotorsport.co.uk/p6927/...duct_info.html)

Anyway, sure enough all put back together again and discovered that if roll on the throttle quickly (i.e. accelerating 0-30mph) the bike feels like its 'starving' or not getting enough fuel to it (to the point of almost stalling a few times).

I've drilled two small holes into the cap under the tab, any other useful suggestions to help bring some life back into her?

Cheers guys

Ant

try running it with the cap open (only for a short period) and see if that helps.

Yes it helps, then its a vaccume issue and you need more venting. Get your drill out and have at it. BTW...make sure your drilling at a location so as to allow venting and not in an area where the cap still seals the hole off.

No it does not help, its an issue with fuel delivery and not effected by the cap. Now you get to start taking things apart.

Yeah, looks like thats it. have drilled an extra hole in it and will give it another run out once my shoulder has healed up a bit.

if a little bit of water gets in the tank (say if it rains really heavily and a small bit gets in) will that cause me any problems?

might have a play with the seal around the cap also.

Cheers for the advice mate

Ant

Hmm. Have drilled two reasonable sized holes in the cap and run the bike with the cap partially open (so without the seal in place) and not noticed a whole lot of improvement in performance.

i've also noticed that if i roll on the throttle very quickly that instead of the swift increase of power (like say my girlfriends Scrambler gives) the bike starts to choak, the exhaust pops and then i get a release of power (kind of delayed) - this is usually when it's at neutral.

the only other changes i've made to the bike (apart from the tank) is that i'm packing short TORS. That and the petrol is slightly pink from what i assume is residue from the sealant (but apart from low end acceleration the bike seems okay with it in there).

Done so far (i.e. within the realms of my ability) :
taken off the petcock and cleaned the filter
taken out the 'hidden filter' entirely

Is there any more 'scientific' way to work out whether it's there's not enough venting for the tank or whether i need to mess with carbs?

i.e. will a Dyno run (which for me is a mystical thing that involves special magics) identify the problem area?

looks like the Aero caps can fit small inline vents so it's the choice whether to get a couple of them to increase the air flow further (£15 a vent) or start the first steps into messing with fuel/air stuff.

any advice is mucho appreciated

Ant

Gutting, and there was me hoping it was going to be something simple

Is there anything i can put through the tank to flush through it? maybe something's getting clogged up that can be dealt with through a lazy approach? Did you have any probs with yours when you pinkified the fuel?

Gonna build in another vent into the bike anyway just in case and then continue the hunt.

just a thought... but I was at work till late last night...so could be barking up the wrong tree...

when you did the tank sealing, you did put a 'something' through the tap attachment bit to stop it getting blocked, didn't you?

Did you eliminate the original fuel vent altogether? I'd think you could test the fuel flow by running a hose out of one of the carb bowl drains (into a suitable container) and opening the set screw valve and observing the flow. I'd also be tempted to clean the carbs just to insure the tank sealant hasn't fouled one of the jets.

Gina - you mean did i do the sensible thing and protect the petcock from getting gummed up with sealant? nope!
but i was careful where i 'sloshed' it (my main concern was the freshly welded area at the top of the tank) and when i took the petcock area apart it had a bit of grub..but no sealant anywhere on it.

Oldroadie - from what i can see (i didn't do the welding) the origional pipe that runs from the bottom of the tank to the top is still there but blocked off at the top (i think he mentioned he'd welded it closed). I've pinged him an email to get a bit of clarity but i think that route's out unless he's only sealed off the top end and it can be snipped off.

or am i thinking of something else? (the vent at the bottom front right of the tank yeah?)

I'll check out the carbs next - never played with them before so it'll be a bit of a learning curve!

cheers guys

I am going out on a limb...but I seem to remember reading some where that this:

"i've also noticed that if i roll on the throttle very quickly that instead of the swift increase of power (like say my girlfriends Scrambler gives) the bike starts to choak, the exhaust pops and then i get a release of power (kind of delayed) - this is usually when it's at neutral."

is a rich condition, too much fuel.....It seems like you have determined by running with the cap off that you are not starving for fuel....

One other thought is maybe some of the sealant got into the floats and they are off

I re-read everything...I don't see any thing about you running the bike with the cap open...If you did what happened ????

The few times i've tried it i have to confess i'm not noticing a massive difference between cap off and cap on (i've been off the bike for a bit with shoulder problems and coming back onto it i'm finding it hard to work out).

regardless i'm going to fit a new breather to the tank (much like the old cafe racers) and then start a process of trying to improve whatever it is i've done to it.

so far things to check

-is it running rich?
-clean floats?

anything else?

Two other thing I can think of:

1. Clean the fuel screen in the tee between the carbs
2. I have heard that water can collect at the end of the vent tube and block it off or check the rubber vent tube and make sure it is free

1. is the hidden one yeah? i've pulled that one out - not replaced it yet but i've just picked up a clear inline one (your post reminded me to get one) from hein gerike - no crud was in the original one.

2. currently the vent tube is useless anyway as the vent in the tank is blocked off - waiting for delivery of a new 90 degree vent thingy which we're going to bolt on the top front of the tank and then redirect back down the original tube - fingers crossed that helps!

man, i hope i don't have to have a crash course in messing with my carbs!