Topic: heat and loss of power

[tony sawyer]

hi havn't been around for a while .posining a question for the learned collective at sohc4 especsily those racing in a hoter parts.
the british summer is apon us the track temprature is rising
this is when my heat problem start
it seams like last year as soon as it raises o above 25centigrade my outfit seem to lose power when hot ,engine dies without reving
im wondering if its a carb problem jetting i'm running 31mm cr's or could it be fuel evapourtion
we dyno at 81bhp at a very cool dyno room
think got to fit a bigger oil cooler

any experience similar problem or have a solution

[Tintop]

Where is your fuel pump located??  Could be vapour lock if the pump is getting heat soaked by the engine.  A couple of bikes over here have had that issue last year when it got above 25C.

[tony sawyer]

the pumps not on direct heat its on the platform but its food for thourght thanks for responce cbr600 ticker pump

[bear]

I'm with Brian on this one.
Fuel delivery will most likely be the problem.
25 deg? How are you going to handle 40 over here in January Brian?

Cheers,
Brian

[scottly]

If you consider 25C hot, what was the temp in the "very cool" dyno room? Also, vapor lock can happen anywhere in the fuel line, where a bubble of air can be trapped.

[bear]

We run 33CR's.
Engine temp. and fuel delivery are two major problems down here.
We run the biggest cooler we can comfortably fit and partly screen it off in the colder weather.

Our fuel system consists of two Facet pumps installed in series,  wired separately ie two switches.
12mm fuel line to a small header tank (about 400ml) then a 10mm return line back to fuel tank.
The return line is fitted with a tap which can be switched off to force the system to operate at the fuel pump's max pressure if required.

This system gives us a very flexible fuel delivery system.

◆Normal race conditions,  1 pump on return line tap open

◆Hot weather, both pumps on return line tap open. (Increases fuel volume to reduce fuel temp. & vaporization.)

◆Track with high speed corners, 1 or 2 pumps on return line tap off. (Increases delivery pressure to stop fuel surge.)

Hope this might help.

Cheers,
Brian

[Tintop]

I'm with Brian on this one.
Fuel delivery will most likely be the problem.
25 deg? How are you going to handle 40 over here in January Brian?

Cheers,
Brian

Seems to me it was only 22C at the last PI Brian.  Our July race last year was over 30, lost a couple of pounds, but that only makes the rig faster.

If you consider 25C hot, what was the temp in the "very cool" dyno room? Also, vapor lock can happen anywhere in the fuel line, where a bubble of air can be trapped.

+1 scottly  I'd also take a look at fuel line routing, from the pump to the carbs.

[bear]

I'm with Brian on this one.
Fuel delivery will most likely be the problem.
25 deg? How are you going to handle 40 over here in January Brian?

Cheers,
Brian

Seems to me it was only 22C at the last PI Brian.  Our July race last year was over 30, lost a couple of pounds, but that only makes the rig faster.

PI January mate, you can get four seasons in one day.
18deg and raining in the morning, then 40deg and windy in the arvo. 

Cheers,
Brian

[tony sawyer]

thanks for responce thats a couple of points to look at
have you reduced the needle valves on the cr's
had a lot of agro with facet pumps went back to a ticker which maybe the the cause

[bear]

thanks for responce thats a couple of points to look at
have you reduced the needle valves on the cr's
had a lot of agro with facet pumps went back to a ticker which maybe the the cause

We run methanol so our needle valves are on the large side.
I think the secret to using Cr's with facet pumps is the recycling fuel delivery I mentioned in the previous post.
I think the facets can be a little dodgy when it comes to reliable pressure management, but they produce good volume.

Cheers,
Brian

[Tintop]

PI January mate, you can get four seasons in one day.
18deg and raining in the morning, then 40deg and windy in the arvo. 

Cheers,
Brian

So pack long johns, and shorts is what your saying.

As for 'dodgy' fuel pressure, I always run a pressure regulator with a gauge (between pump & carb), and use a pump that's rated about 50% more than I need.  A surge tank is helpful, but baffles, or foam in the main tank can make a big difference to getting consistent fuel pressure.

[scottly]

Tony, are you noticing a serious loss of power, then the rig runs better after cooling off? If so, are you running a Dyna ignition?

[tony sawyer]

no got a simple boyer
is there an inherant problem dyna and heat?
 je pistons two ring hi comp   cx 7 cam
we're moving the pump and putting it upright for starters

[Tintop]

no got a simple boyer
is there an inherant problem dyna and heat?
 je pistons two ring hi comp   cx 7 cam
we're moving the pump and putting it upright for starters

Sounds like a good start.  From my experience electric fuel pumps only operate properly when mounted as originally intended.

The Boyer's either work or they don't, although I did have an issue with mine.  Cause was the wires from the P/U plate (7/10 yrs old) had become brittle from heat (cracking insulation) and I started to get intermittent ignition cut-out.  Replaced P/U, problem solved.  The Dyna S had issues (couple of years ago) failing from heat under the points cover.