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Question about fuel tap and bullet 500 cruising speed..
Posted: Sat Mar 27, 2021 9:50 am
by jawa-enfield
Okay, done my first 700 km's on my freshly rebuild bullet 500 with 19T sprocket.
engine is running fine.
I've read somewhere/someone told me that 100km/h cruising speed is very well possible whitout destroying the engine with a 19T sprocket.
But i must say at 90km/h, it is already revving quite high?
Fact is, i've always been a little afraid of high revving.. (that's why i also have a diesel enfield..
)
Question one, is 100km/h normally 'safe' for the engine?
Question 2; At the moment it has a fuel petcock whithout reserve, but with very good flow.
I want to keep this in the running in period, because if an other fuel tap restricts too much (at higher speed, where it needs more fuel) and gets a piston jam..
Beside i have a jawa fueltap (the originals were often restrictive for a jawa, the imitations are better) and this one from our host.
https://accessories.hitchcocksmotorcycl ... rt%20500cc
My question No. 2;
Can it be too rerstrictive? Are there any reports about it?
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sat Mar 27, 2021 12:54 pm
by vince
Hi, dont know why the later bullets would be different but my 1956 bullet would cruise at 70mph (115kph) without any problem, as most british 500 of that period could. Vince
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sat Mar 27, 2021 6:31 pm
by Adrian
19T on an otherwise standard 500 Bullet is rather high gearing, so you will HAVE to use more revs, otherwise you risk "lugging"the engine (running it at too low revs for its gear, particularly in 4th gear). The normal 17T gearbox sprocket gives you a top gear of around 5:1, which is more or less the same as the 500 Redditch-built Bullet.
If there is no adapter in the fuel tank you will need a good pet-cock (petrol tap over here) with a ¼" BSP thread, our hosts have some, any British motorcycle specialist will also have them. I'd be surprised if Jawa used an imperial thread anywhere.
ANY tap has to have a decent flow, and for that reason avoid the cheap Indian taps like the plague. Our hosts sell a tap which is suitable for Methanol, which really does need a good flow, so it will be plenty good enough for keeping your 500 supplied with enough fuel. Part No. PTAP2.
A.
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 7:43 am
by ChrisD
Hi Jawa-Enfield
I’m glad you have started this discussion. When I first suggested you needed better flow for a tuned Bullet than the available taps, potentially getting perhaps less than 20mpg at wide open throttle (WOT) at high speed, I was ridiculed.
Tests carried out on my 1996 535cc Bullet (9:1, twin plug, 32mm Mk2Concentric, ported head, largest valves, 19T sprocket etc) show the following (all in top gear).
Pobbling along at ~2000rpm or ~55kph, I use less than 2litres/hour or 30-35ml/minute which equates to 80-90mpg.
On a normal ride, with freeway cruising at 1/3 throttle at ~100kph, I get 18-19kms/litre or ~55mpg.
I know at WOT at over 130kph (80+mph) I get far less than that. I haven’t had the courage to hold that speed for long enough to confirm this, but I’d bet it could be 6-8kms/litre.
Putting those numbers together, at WOT it would take way less than 3-4 minutes to use a litre or 250-330mls/minute. The OEM indian tap managed 180ml/min after drilling out.
I also noted that the glass bowl filter (PN 90007) froths like mad at high revs, so reducing the available flow – hence its removal.
I have one of Mr H’s hexagonal taps with reserve (PN 36583) which delivers better flow than I need (actually measured at 420mls/min) but only after I had drilled out the tap bore and sliding plate by ~1mm and installed nitrile seals!
Cheers, ChrisD
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 8:50 am
by jawa-enfield
Adrian wrote: ↑Sat Mar 27, 2021 6:31 pm
19T on an otherwise standard 500 Bullet is rather high gearing, so you will HAVE to use more revs, otherwise you risk "lugging"the engine (running it at too low revs for its gear, particularly in 4th gear). The normal 17T gearbox sprocket gives you a top gear of around 5:1, which is more or less the same as the 500 Redditch-built Bullet.
If there is no adapter in the fuel tank you will need a good pet-cock (petrol tap over here) with a ¼" BSP thread, our hosts have some, any British motorcycle specialist will also have them. I'd be surprised if Jawa used an imperial thread anywhere.
ANY tap has to have a decent flow, and for that reason avoid the cheap Indian taps like the plague. Our hosts sell a tap which is suitable for Methanol, which really does need a good flow, so it will be plenty good enough for keeping your 500 supplied with enough fuel. Part No. PTAP2.
A.
The tap i mean i the one in the link in my first post, and yes it has an adaptor.
https://accessories.hitchcocksmotorcycl ... rt%20500cc
Strangely enough, i could fit a jawa tap on my enfield diesel tank whithout a problem?
Frther, i thought 18T was std for the 500?
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 8:55 am
by jawa-enfield
ChrisD wrote: ↑Sun Mar 28, 2021 7:43 am
Hi Jawa-Enfield
I’m glad you have started this discussion. When I first suggested you needed better flow for a tuned Bullet than the available taps, potentially getting perhaps less than 20mpg at wide open throttle (WOT) at high speed, I was ridiculed.
Tests carried out on my 1996 535cc Bullet (9:1, twin plug, 32mm Mk2Concentric, ported head, largest valves, 19T sprocket etc) show the following (all in top gear).
Pobbling along at ~2000rpm or ~55kph, I use less than 2litres/hour or 30-35ml/minute which equates to 80-90mpg.
On a normal ride, with freeway cruising at 1/3 throttle at ~100kph, I get 18-19kms/litre or ~55mpg.
I know at WOT at over 130kph (80+mph) I get far less than that. I haven’t had the courage to hold that speed for long enough to confirm this, but I’d bet it could be 6-8kms/litre.
Putting those numbers together, at WOT it would take way less than 3-4 minutes to use a litre or 250-330mls/minute. The OEM indian tap managed 180ml/min after drilling out.
I also noted that the glass bowl filter (PN 90007) froths like mad at high revs, so reducing the available flow – hence its removal.
I have one of Mr H’s hexagonal taps with reserve (PN 36583) which delivers better flow than I need (actually measured at 420mls/min) but only after I had drilled out the tap bore and sliding plate by ~1mm and installed nitrile seals!
Cheers, ChrisD
Ah these ones.. no longer available..
Yes i am scared of running too lean when engine is working hard..
And yes, i think the bulk of the bulleteers are happy trundling along at max 80 kph and will do fine with the 'normal' tap.
Still, i am scared revving it over 90km/h on tjhe ode (is ca. 85km/h on navigation device) because of the high rpms..
I even have this with my diesel..
I am happy both my bullets don not vibrate at higer (or lower) revving..
Some foilks report sometimes otherwise?
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 9:00 am
by PeteF
19 tooth is too big on a standard Bullet IMHO
I've been there and reverted to 18 which is still quite tall enough.
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 9:32 am
by Bullet Whisperer
Gear them up to the hilt to lower the revs, then the engine will die sooner under the extra strain, with accelerated big end wear, higher internal temperatures, which in turn will give rise to pinking and exhaust valve / seat burning. There is really no way a Bullet could be doing 'high revs' at 100 kph, which is what - about 65 mph?
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 10:01 am
by jawa-enfield
Okay.. so the tip/advice to mount a 19T sprocket was not so good?
In defence of the engine; it has a M20 muffler (absorption) PWK 28mm carb and open (paper unit) air filter.
It does accelerate in 4th gear though..
But, with the 18T sprocket, what is considered a 'safe' cruising speed for the engine?
Re: Question about fuel tap and bullet 500 cruising speed..
Posted: Sun Mar 28, 2021 10:30 am
by Bullet Whisperer
I would be happy to do 60 -65 mph as a cruising speed on a 500 Bullet running a 17t gearbox sprocket, so based on how you describe your 'state of tune', an 18t would probably work well with it. I recently tuned an Electra X which already had a 19t sprocket fitted, the owner didn't realize and brought another 19t sprocket with the machine for me to fit and I told him it would probably be better with the standard [for these machines], 18t sprocket fitted, as it goes very well to around 80 mph in 4th, but 5th is a little tall, it will accelerate, but not as well as it would on slightly lower gearing when in top gear.