Throttle cam question 50D2

[Tigerbeef]

We have a Tohatsu MD50D2 that we race thundercats with. All the other racers are using a different throttle cam than the one sitting on ours.

The difference is that the apparently older type of throttle cam is one-piece and more or less linear on both timing advance and throttle plate trough the throttle range, but the 2-piece one we got is only moving the timing at the low end of the range and the throttle plates are not moving much until the timing advance hit full timing and then the throttle plates start to move considerable amount.

Why is this different? Would this affect performance? Is this some kind of emission regulation thingy?
Is this older one-piece still on the shelf?

And while I am at it; Second topic aswell...

We are wondering about the spring loaded needle screw on each carburetor, what does this do?
Thorough explanation would be much appreciated.

Asking because we are tuning it and are going to synch the carbs with vacuum gauge.

Thanks, by the way new to a excellent forum from first impression.

 

[Sea Rider]

Re: Throttle cam question 50D2

You could ask other racers if they have changed their throttle cam for the one you describe, probably have so for racing, the spring screws are air/gas mixture for each carb and probably a second one somewhere that adjust idle speed on all 3 carb at same time. For sure will find someone skilled on that model who will assist you.

Happy Boating

 

[Tigerbeef]

Re: Throttle cam question 50D2

We have asked them about this but they seem somewhat interested to keep some things for themselves, that's racing. I am sure there are a tohatsu guru here somewhere who can shine a light at this matter. hint.hint.hint

Adjustment screw for air\gas mixture? Does this adjustment apply to the whole rpm range or is this adjustment for idle and\or low speed. Is it this screw we use to synch the carbs?

 

[Bobbyjoeufb]

Re: Throttle cam question 50D2

You might be worth while getting hold of a service manual for you engine and check out the tune up / carb synch.

It all involves measurements of the linkage that connects all three carbs to ensure that on WOT all three buttleflys are in the fully open postion.

Have a look on http://www.thundercatinflatable.com.au/forum/ very good source of information also a download link for the service manual.

 

[Tigerbeef]

Re: Throttle cam question 50D2

We have the service manual, but it slightly unclear on some of the adjustments. We started with setting the links to specified lengths and then adjusted all the butterflies to all be closed at idle and all be fully open at wot. Then we adjusted the throttle lever screw on the top carb to specified number of turns, at last we sorted out the timing to spec.

This done so far is very accurate adjusted and we are happy with this. Everything is smooth and with no slack.

But at this point things get unclear in manual, because there is no explanation furthermore using vacuum gauge to fine sync the rest. It do not explain what to do and what adjustments on this gas/air mixture screw do and if it is indeed this screw we should use when syncing.

Still nothing is mentioned in the manual regarding this throttle cam difference.

note; We both are car mechanics with years of experience. But 2-strokes are pretty new to us, tough we do of course understand most of the stuff.

 

[Sea Rider]

Re: Throttle cam question 50D2

The air gas mixing screw is for each carb idle /ralenti speed as all 3 carbs have fixed wot jets, don't know if a vacuum gauge could be applied to each carb to fine tune as in cars, would be fantastic if you could.

If it's a throttle racing cam, won't even be mentioned in the manual, you'll need to get a Tohatsu Racing Guru that sheds the light at the end of the tunnel, good luck.

Happy Racing

 

[deejaycee_2000]

Re: Throttle cam question 50D2

You can just adjust the throttle cam and adjust to advance the timing, I race a D2 blueprint tohatsu .... have you done the carb float mod and what jets are you running, switch to 125 jets will increase performance ....

 

[TOHATSU GURU]

Re: Throttle cam question 50D2

Tigerbeef,

What's the serial number of your engine?

 

[Tigerbeef]

Re: Throttle cam question 50D2

I do not have the serial number now, can post it tomorrow. But engine is a 2005 or 2006 MD50D2 as are most of the other teams engines also.

But did find out what part they use. They switch out 3E3-63718-1 witch is original on the D2 with 3E3-63718-0 witch was used on earlier MD50D. They mention that this older part is also available from nissan and mercury 50s.

But are having a hard time finding this part.

Regarding syncing carbs with vacuum, this went as a dream. Really good tool, idle and low speed is really smooth and vibration less. Starts on a half pull cold.

Another thing, we used the three couplings on the reed cage for vacuum, and noticed that the three throats are connected to each other with full venting from one to another. Speaking 2 stroke witch is very dependent on vacuum behind the butterfly, is this venting optimal? Asking because it really purred like a kitten when each of these joint were connected to a vacuum gauge. and not connected to each other

 

[TOHATSU GURU]

Re: Throttle cam question 50D2

The 3E3637180 was replaced by the 3E3637181...So its not available from Japan. Your local dealer or the distributor for your country might have one laying around. If I remember correctly the "venting" is part of the fuel scavenging system to prevent gas spills and save fuel....I might be wrong though. You should contact the Tohatsu distributor for your country for a definitive answer.