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DC conversion

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3 months 2 weeks ago #20951 by ConradNordquist
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I've converted my 503 to dual carbs, set up per manual. Installed an electric fuel pump in line (series) to the pulse pump. (My fuel head is only a few inches) With lots of priming the engine starts and runs fine at 3000 or more, but when I bring it to idle, 2000 rpm, it runs smoothly for a while (30-90 seconds) then begins to slow down and finally die. It does this with the electric fuel pump running or off. Once it starts to die, opening the throttle doesn't have any effect.
What am I doing wrong? Any suggestions?
Installation manual recommends pumps be parallel, but I think that would be too much fuel pressure.

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3 months 2 weeks ago #20960 by nickjaxe
Replied by nickjaxe on topic DC conversion
When it stops look at the fuel level in the carbs bowls see if the level is low or high and both the same.

Nick.
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3 months 2 weeks ago #20961 by Bill Hertzel
Replied by Bill Hertzel on topic DC conversion
You have a problem that is not a Series/Parallel issue.
Before the start, enough fuel dribbles in by gravity to fill the carb floats.
It may be that once started there is not enough fuel being delivered to keep the carbs full and after a minute or two, the carbs run out of fuel.

The first thing to confirm is that the Fuel Filter(s) is/are not blocked.
Pull a hose off of one of the Carbs.
Turn ON the Electric fuel pump.
The pump should deliver a Quart to Half a Gallon of fuel into a gas container in a minute. Time it.
If it just a trickle, start opening the fuel lines to find the restriction.
It will typically be the fuel filters, the input connectors of the fuel pumps, or the upstream side of any other fuel fittings.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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3 months 2 weeks ago #20962 by Bill Hertzel
Replied by Bill Hertzel on topic DC conversion

nickjaxe wrote: When it stops, look at the fuel level in the carbs bowls see if the level is low or high and both the same...


Also a good idea!
I might add that you will want to turn off the fuel shutoff valve Immediately after the engine quits or a slow flow of fuel may refill the floats before you can get them off and mask the problem.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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3 months 1 week ago #21133 by ConradNordquist
Replied by ConradNordquist on topic DC conversion
Still having trouble with my nearly new 503 DCDI. It will run ok at 3K to 5K, but refuses to idle. I've varied the idle air screws from 1/4 out to 1 turn out with no difference. I've blown out the idle jets and all holes look clear. Fuel flow is good, 30 gph at the pulse pump from the electric pump. It won't start without priming, even when warm. All plugs show a spark, but cyl.#2 runs much cooler than #1. Air temps are around 70 degrees F., altitude 800' so it's close to standard day. I have catalog recommended jets, needle, etc.
I think I may have an ignition problem, weak spark on Cyl #2, as well as a carburetor problem.
I've addressed all the recommendations you've previously given and still no luck. I'd welcome suggestions, ideas, or contacts who can look at the engine in Southern California.

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3 months 1 week ago #21136 by nickjaxe
Replied by nickjaxe on topic DC conversion
When you say wont start without priming...what do you mean by priming...

Weak spark...is that observer the plug while you crank...and is it both plugs they you say have a weak spark.

Nick in the UK.

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3 months 1 week ago #21142 by admin
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You can use this link to find iRMT techs in your area:

rotaxirmt.com/locator

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3 months 1 week ago #21143 by ConradNordquist
Replied by ConradNordquist on topic DC conversion
Nick, thanks for your input. By priming I mean 3 to 6 strokes on the Rotax priming pump that goes to both carbs. By weak spark I mean that the plugs from cyl # 2 are wetter and not as hot to the touch as those from cyl #1 when removed right after shut-down.

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3 months 1 week ago #21145 by nickjaxe
Replied by nickjaxe on topic DC conversion
Do you have duel CHT...if so how do they compare...for that matter how do the EGTs compare.

Next time it stops on you drop the carb bowls to see where the level is...you need to see if its dropped...sounds like it prob will have if you need to prime up.

Could there be anything restricting the flow...such as a kinked fuel hose maybe a part blocked fuel filter ect.

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3 months 1 week ago #21148 by Dennisr5
Replied by Dennisr5 on topic DC conversion
Your 503 may be low hour but it is at least 8 years old. 2 strokes hardly ever wear out but usually die from improper storage. The symptoms you describe could well be a crankcase seal problem.
Dennis
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3 months 1 week ago #21154 by ConradNordquist
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Thanks Dennisr5. I'll look into it.

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3 months 2 days ago #21210 by ConradNordquist
Replied by ConradNordquist on topic DC conversion
Thanks to all of you who have given me advice. I contacted a Rotax mechanic through the website who worked through the problem, (9 hrs at $95/hr) finally getting to the crankcase seal test. When removing the carb manifolds we found one cracked and broken. Further pressure testing and smoke testing showed no further leaks so we buttoned it up with a new manifold and it idles perfectly! Problem solved.

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