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A little more on the IOM Le Mans


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Hello Again,

 

After we returned from Miller the team all got together and took time to discuss the weekend and the results.  The bottom line is we improved all through out the weekend but we are still getting beat.  In the last race Wade our rider took on the entire field and got the bike into and through turn one in the lead.  And that's the good news.  After that we kept getting passed until we ended the day in third as I posted before.  We finally have come to the conclusion that our problem is in the gearing.  Gina (our pet name for the motorbike) was built for the Isle of Man, Wade has nearly 20 years racing there and after many an hour going through the strengths and weaknesses of the Moto Guzzi we made it our main focus to make time in the fast and very fast sections of the Island.  One of the things that we did was find the tallest gearing available.  There in may have been a fine idea for Manx GP but not the best for short courses.

 

Wade had said that at Miller (we were racing what is know as the East Course; which is very tight indeed) that he could rarely click top gear.  So now our focus has changed.  We first know that our rider is quick off the line and as he get more intimate with Gina and her Italian proclivities he is going faster every event. So we shall begin to work on improving his corner exit speeds.  Top end at Daytona (by their Radar gun) was 150 so she's not slow but she ain't very quick to get her skirts gathered up and down the road

 

Ed from Guzzi Power has been a great help to us and tomorrow I'm heading down to his shop for a lower final drive.  Based on the ratios it should be about 14% lower that what we have been running.  We plan on one last test prior to loading everything in the crate for shipment to OZ and I'll let you all know how that test worked out.

 

Cheers

Rich

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Back at Ya,

 

Will see what I can do about pics.  Tons of folks came by and were taking pics but I was kinda focused on the motorbike.  I think that Eric on our team  (Because of Gina's PURPLE tones we have become known as the PURPLE GANG) may have taken some.  I'll chat him up and see what I can do.

 

Thanks for your interest.

 

Oh, almost forgot.  As I went back over our notes from Miller I noticed that we seem to be loosing speed at the end of the straights.  Talked to Wade the rider and he said that he would chop the throttle when she stopped pulling and then hit it again and she'd start pulling again.  I went back through the fuel system plumbing and I think that we may be running out of fuel at full power on long straights.  There are a multitude of fuel petcocks for the Guzzi, Aprilia and Docks so my question is:  does anyone know the OEM size  (16mm (1.0 TP female nipple ) with the largest exit barb ?  The ones that came with the tank look to be about 1/8" and even as we are using one for each carb I think there in is the problem.  Anyhow any ideas would be great.

 

Cheers

Rich

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  Anyhow any ideas would be great.

Ok, I'm having a hard time imagining chopping the throttle and opening it letting the float bowl fill to a measurable degree. How about a sticking advance or something involving ignition?

Well, you did say any ideas.. :huh2:

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Chuck,

 

Keeping in mind that nothing on the engine is OEM it can't be electrical as the ignition is all electronic.  The engine does not really run totally out of fuel but rather goes into a fuel starve mode.  What Wade told me was that it starts to fall off and as soon as he backed off and hit it again it would pick up.  When I checked all the fuel related things, from the tank venting to the float height what seem most out of what I call spec is the size of the petcocks.  Everything else was looking correct.

 

The only other cause we consider would be vapor locking (weather was quite hot and 4400 feet altitude) we are doing what we can to make sure the fuel is not subjected to boiling.  Still as soon as Wade came into the paddock the engine ran fine and started fine.  Vapor locking usually requires time for the vapors within the system to dissipate there by allowing liquid gas to enter the system.

 

Thanks for the thoughts and do keep them coming.  I learned about how vapor locking works from a guy how restores vintage cars.  These have the problem and he PM'd me the information.

 

Cheers

Rich 

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Don't the carb accelerator pumps add that extra fuel when you close and reopen the throttle. Perhaps it just needs bigger jets. There again shutting off at high revs means the inrush of air cannot all go into the engine, instead it semi pressurises the ambient air side and reduces the fuel entering the float bowl so you need a fuel pump, bit like a blown motor.

Have fun.

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68C,

Not really how these carburetors function.  Fuel tank is the large fuel reservoir and the float bowl is more or less the small fuel holding tank.  Fuel flow between the two is controled by a needle valve and float.  Fuel flow is from gravity.  The carb needs float bowls because fuel use is  always fluctuating.  Electric fuel pump easily over power the needle valves and when used are controlled by pressure regulators set at very low PSI.

 

After examining the fuel system our conclusion is that the problem (this is often the case) is from several inherent weaknesses.  Remove any one and we most likely we would have been OK.  They things we found are as follows:

 

Fuel tank has very poor venting.  We were racing in two events back to back so we filled the tank to the top.  At 4500' this may have caused the tank to not vent properly.

 

Fuel lines need more protection aginst heat:  The fuel lines cross the frame above the engine and are exposed and heat coming off the oil cooler.  This can cause the fuel to become a vapor either in the lines or filters.

 

The two fuel petcocks that are on the tank may have come from a Guzzi with smaller displacement.:  The petcocks have very small exits the ones we have ordered are better than twice the size.

 

The fuel petcocks have three positions on, off, and reserve it would be very easy to inadvertently push the lever to reserve.  The reserve orfice is half the size of the main orifice.   

 

We are in the process of fixing  all these issues and here in is the reason we have been racing the bike anywhere we can before shipping it off 12,000 miles from home.

 

For me this is always the fun part of racing so I don't mind the work here,  Wade the rider may feel a tad different.

 

Cheers

Rich

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Being a public school graduate math was never my strong point. I do believe you can calculate the flow rate from the petcocks to what the carbs are capable of moving. I think you are on the right track installing larger petcocks and larger diameter fuel lines. You can't get too much fuel delivered to the float bowls. But with the engine at full throttle I'm sure it can suck the bowls dry. Are you running stock needle valves in the float bowls? That might also be a source of fuel restriction, combined with the tank vent.

The proximaty of the fuel line to the cylinder head my 02 LeMans always concerned me as many owners complained of vapor locks so I purchased a woven and foil covered fuel line insulation kit by DEI from a local hot rod shop. Even in our Florida heat and humidity I have not had a problem.

Thanks for sharing, I really enjoy your write ups.

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JRD,

 

Glad you like the write ups.  We are not running OEM carburetors.  As the rule allow for the change we have switched to Mukuni's.  The reasons for the change is multi faceted; we already had a large supply of jets, gaskets, needles not to mention the Muki's flow better. 

 

We also are considering more heat protection for the fuel components.  I am even considering making small (4" X 4") shields to go between the carbs and the cylinder fins.

 

I totally agree that just looking at where the heat is generated and where the fuel is moving makes me wonder if vapor lock could be part of the problem.

 

What is most strange is the fact that we raced the bike at Willow Springs (high in the California (2500') desert  ) with no fueling problems.  The one thing we did different was filling the tank to the very top because of the back to back races.

 

Thanks for the feed back.  Every idea helps as we work towards getting Gina up to speed.

 

Cheers

Rich

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JRD,

 

Glad you like the write ups.  We are not running OEM carburetors.  As the rule allow for the change we have switched to Mukuni's.  The reasons for the change is multi faceted; we already had a large supply of jets, gaskets, needles not to mention the Muki's flow better. 

 

We also are considering more heat protection for the fuel components.  I am even considering making small (4" X 4") shields to go between the carbs and the cylinder fins.

 

I totally agree that just looking at where the heat is generated and where the fuel is moving makes me wonder if vapor lock could be part of the problem.

 

What is most strange is the fact that we raced the bike at Willow Springs (high in the California (2500') desert  ) with no fueling problems.  The one thing we did different was filling the tank to the very top because of the back to back races.

 

Thanks for the feed back.  Every idea helps as we work towards getting Gina up to speed.

 

Cheers

Rich

I dont think vapour lock will be an issue as the fuel is moving through the lines at a rate that precludes this. I've had bikes that vapour lock and its only ever happened when the bike is stationary fully warmed up on hot days. During normal ops they have been fine.

There is an actual calculation for required fuel flow from memory so you can work out for the power you are generating what fuel flow you require and measure what you have with a stop watch and container.

 Edit.....try this. I havent had time to go through it and it wasnt the one I was thinking of but you get the idea. My back of the envelope calculation for a 100hp engine is 16 litres/hour (gas) so if your taps will flow half each of this you're golden. You should also check the needle valves will flow enough as well of course and the venting is capable. 

http://blog.cantonracingproducts.com/blog/how_to_estimate_your_engines_fuel_flow

Ciao

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I would think the biggest limitation on fuel flow would be the size of the main jet. I can't believe that the petcock can't flow as much fuel as your main jets can if it is clean and in good shape. Next limit on fuel flow would be the needle valve that lets fuel into the carb float bowl. The size of that opening determines how much fuel can get into the carb. Again, I can't believe that your needle valves can flow more fuel than your petcock if it is clean and in good shape.. But a dirty or clogged petcock, or needle valve, could be an issue.

I suspect the behavior your seeing has to do with fueling, and closing the throttle and re-opening it may be adding extra fuel. But it may be simply that your main jets are not big enough. Fueling issues can be hard to figure out. But I have my doubts that your petcock is the root of your fueling issues unless there is something physically wrong with it. Here is a simple test, pull the fuel line of the carb and let the fuel run into a bucket. You can see the max rate of flow that petcock supports. It is likely that it will flow more fuel per minute than your motor can consume. You can actually measure its flow per minute if you want.

If that flows enough fuel, do the same test but do it at the carb. Meaning, pull the float bowl off the carb with it in a bucket and see how quick the fuel flows into the bucket. As before, you can calculate the fuel flow per minute and see if it is more or less than your max fuel consumption per minute at WFO.

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  • 2 weeks later...

Checking back in.  And again thanks for the ideas.  The bike had spend quite a lot of time on the dyno and had never had a fueling problem so under these conditions  I ask myself what things are different from the dyno run and running on the race track ?

 

1.  Ambient temperature is different  (high 80's verses 100's) BUT when we raced at Willow Springs it was in the 90's ??

2.  We were at 5000 feet in altitude Willow Springs is around 2000'

3.  We were getting our fuel from a MotionPro fuel bottle rather than the Moto Guzzi tank

4.  The Miller course was lots of short straights and tight corners.

 

Because the motorbike spent so much time on the dyno I can't think how the carburetors could be at the bottom of the problem.  Not once did we see the engine act as if it was fuel starving.  The last few pulls were all right on the money as far as the sniffer readings indicated  and the engine kept pulling as many RMP as we dared to ask of it.

 

One thing we found as we pulled the motorbike apart was that the petcocks that came with the fuel tank (they looked to be fairly new) were very small 1/8" and the ones for the big motors are twice as large.  When I asked the local MG guys I was told they came off a fairly small engine bike maybe no bigger than a 650cc. 

 

At this point all we can do is attack all the things we thing might be at the bottom of the problem and test again at the last AFM race at T-hill in North Ca,

 

Thanks again for the input.

 

Rich

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  • 1 month later...

I would think the biggest limitation on fuel flow would be the size of the main jet. I can't believe that the petcock can't flow as much fuel as your main jets can if it is clean and in good shape. Next limit on fuel flow would be the needle valve that lets fuel into the carb float bowl. The size of that opening determines how much fuel can get into the carb. Again, I can't believe that your needle valves can flow more fuel than your petcock if it is clean and in good shape.. But a dirty or clogged petcock, or needle valve, could be an issue.

I suspect the behavior your seeing has to do with fueling, and closing the throttle and re-opening it may be adding extra fuel. But it may be simply that your main jets are not big enough. Fueling issues can be hard to figure out. But I have my doubts that your petcock is the root of your fueling issues unless there is something physically wrong with it. Here is a simple test, pull the fuel line of the carb and let the fuel run into a bucket. You can see the max rate of flow that petcock supports. It is likely that it will flow more fuel per minute than your motor can consume. You can actually measure its flow per minute if you want.

If that flows enough fuel, do the same test but do it at the carb. Meaning, pull the float bowl off the carb with it in a bucket and see how quick the fuel flows into the bucket. As before, you can calculate the fuel flow per minute and see if it is more or less than your max fuel consumption per minute at WFO.

+1 

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Just to share my observation with my LeMans 2 and 3 (different PHF36 carbs) and the California 2 with VHB30. The california has an old paper air filter. When it gets dirty (7000km+) and i ride full throttle in 5th gear, it starfs a bit on not enough air. Closing the throttle a tiny bit gives it just the extra 5 km/h. This phenomenon fits to a to big main jet. For a touring motorcycle it's okay. It protects the engine for overheating.

 

Especially with the LM3 (850), I reduced the main jet to 125 in order to increase topspeed. It is running a little over 200km/h, which I think is quite alright (almost 8000rpm, redzone). So you could check both a larger or smaller main jet to be sure.

 

Additional anecdote. This is for Super Single race-machines. The engine is right underneath the tank and heats-up the fuel in the tank. This causes a decreasing density of the fuel and thus a decreasing amount of energy/ liter. A racing motorcycle dealer from Amsterdam used an oil-cooler to cool the petrol. This gave him an advantage in the second stage of the race, when others suffered from heated fuel.

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