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Makotosun

1970 RT-1 Carb Woes

  • mwlockwood
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1970 RT-1 Carb Woes was created by mwlockwood

Greetings from the gloomy UK!

I recently purchased a grubby RT1 'ran when parked'. I've given it a complete going over as best I can, installed the VAPE ignition (wonderful) and sourced the correct VM32 carb, genuine Mikuni jets and a genuine Mikuni rebuild kit from the USA. I did the crank seals and fresh gear oil etc.

Trying to get it idling on pre-mix from a crappy DIY aux tank I made. It 'started' 2nd kick and was a lumpy old girl but it was turning and burning and promptly shut off.

I can only get it going with the choke on, and it WILL NOT idle. I have to blip throttle and then it'll shut off.

It feels like it is running out of fuel to be honest. I set the float arms parallel with the bowl as per advice read on here. The tang is resting on the needle spring, but not compressing it - would you agree that is correct?

If I blow down the fuel tube into the carb, it feels difficult. It feels restricted. Is this normal? I blew down my CT1 carb and it felt so much easier, perhaps my bowls are not filling up fast enough?

This is my first carb with sliding floats, and this is the first carb I have had where the needle valve has this little spring over it. It is bloody loose in there when the carb is in operating condition? And it feels like the float arms interfere with the floats! NIGHTMARE.

If you are still here after reading all that, thankyou, and any advice or anecdotes welcome.

One picture shows my carb inverted, to show my float arms.

One picture shows my carb in its running position, with the needle floating about!
29 Mar 2023 12:00 #1

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Replied by Dennis D on topic 1970 RT-1 Carb Woes

Make sure you are installing the floats correctly. Pins on the floats
go toward the bottom of the float bowl with the carb in the upright
position.
The following user(s) Liked this Post: Rick C.
Last edit: 29 Mar 2023 12:45 by Dennis D.
29 Mar 2023 12:42 #2

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Replied by RT325 on topic 1970 RT-1 Carb Woes

Very good point made by Dennis D above!!. Favorite trick 'that' fitting floats inverted. May not be that as think that stops all fuel entering, depending how high the float arm was set so just could be that. Otherwise so long as crank seals went in ok it sounds like something unseen is blocked in the carb, more likely the pilot jet as runs on choke so choke fixed jet in the bowl cavity must be ok. Spring clip on the needle only stops it dropping out when ya fiddling on the bench & disappears under the compressor [at my place lol]. Float arm about level inverted [which you have]. No major air leaks--best of luck. ps, main jet clear--as everything bar the pilot & choke draws from that up the slide needle.
Last edit: 29 Mar 2023 13:18 by RT325.
29 Mar 2023 13:14 #3

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Replied by mwlockwood on topic 1970 RT-1 Carb Woes

Thanks for the quick replies gents.

The floats are the correct way, they even have a little ‘up’ on them but good to know!

Great point about the main jet - I have been so focused on getting that bowl off I haven’t given it a second though.

More more cleaning!
29 Mar 2023 13:41 #4

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Replied by RT325 on topic 1970 RT-1 Carb Woes

Small Oring looks a bit oversize but if its genuine or ya happy its ok then--ok. Just thought if too big it might get rolled out fitting the bowl on. In saying 'that'--that would only send it super rich as bypasses the main jet. Ignore me lol.
29 Mar 2023 14:09 #5

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Replied by Dennis D on topic 1970 RT-1 Carb Woes

If you are feeling a restriction when blowing through the hose,
check and see if the vent tube is clear.
29 Mar 2023 14:31 #6

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Replied by Pedalcrazy on topic 1970 RT-1 Carb Woes

Make sure "crappy DIY tank" is vented or it could be starving out from a sealed tank.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
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29 Mar 2023 16:53 #7

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Replied by mwlockwood on topic 1970 RT-1 Carb Woes

Just wanted to give you guys an update!

I went back to basics and my timing was off - I didn’t do my new vape stuff up tight enough!

Starts and idles OK now… just need to fix a hanging idle and air leak hunt!
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31 Mar 2023 04:10 #8

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