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46 gas tank?

Submitted by nathan_stuch on Monday, 27 February, 2023 - 12:53
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Gents,

took the 46 out yesterday and it seems to run well for the short trip I did around the lake. When returning home I was running around 50-55ish and as soon as I approached a small hill the bike seemed to just run out “steam” and died…I did not even have a chance to down shift. Waited a minute and I then kicked a couple time and started up.  I went about 2-300’ and did it again and repeated the steps and the ran fine rest if the way home but I went a little slower. When I returned home i shut it off for a few and could not find anything lose or that would think to cause it to lose power. Spark plug was tanish gray but gap was at .028 instead of .015 per manual…bought this way.  Magdyno is fresh and has good spark. Did a compression test and got 130PSI. I then read about model H16 having gas tank vents but could not find any pics of this…does the model 18 have a tank vent and if so where is it located since I couldn’t find one. Sorry for the long dissertation but you all have been a great source of help. Thanks.

Nate

 

 

Submitted by david_cooper on Monday, 27 February, 2023 - 13:36

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Mine have a hole in the tank caps.  With a little pierced metal tab below it.  The gasket needs to go around outside the hole and not block it accidentally.  The hole can of course get blocked.

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Submitted by ian_soady on Monday, 27 February, 2023 - 17:00

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... is next time it stops pop the petrol tank open and if you hear a hiss of air entering then that's your problem.

Fading when warm / hot is often a sign of a magneto capacitor on its way out but look for the cheap fixes first!

Submitted by nathan_stuch on Monday, 27 February, 2023 - 23:35

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After a peek at my cap, I have a very very small hole. After looking at David’s picture with one large and one small hole should I drill an extra hole? Not trying to sound lame just curious if this will help?

Submitted by richard_cornish on Tuesday, 28 February, 2023 - 03:37

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Hi Nathan.

   The side-valve engines can often show your symptons due to the exhaust valve expanding when hot. The valve can lengthen so much that it is lifted off the seat and you lose compression. Left a couple of minutes, it will cool enough to start again. See if you can check this, and if so you can just open the tappet 2 or 3 thou extra.

Submitted by robert_tuck on Tuesday, 28 February, 2023 - 05:56

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 If the valve guides have been replaced with "modern" clearances to the valve stems or wrong metals  the extra heat from hill climbing can result in total loss of power as the valves stick. A little time to cool and they return to normal. Continued use will burn out the valve or seat.

Submitted by david_cooper on Tuesday, 28 February, 2023 - 09:14

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That's one hole and a speck of dust!  The usual test is to release the cap and see if that helps immediately.

Robert points out another possibility.  But I think your OHV tappets should be snug when cold, and then open a little as it warms up? So clearance should become wider, unless someone fitted home made alloy push rods (which doesn't seem likely.)

My SV did once suffer similarly to yours because a tappet guide started to unwind itself from the case.  I don't think that applies to OHV, but don't know.

Submitted by ian_soady on Tuesday, 28 February, 2023 - 10:09

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.. was a pig to start within a few minutes of stopping. A kindly passing ex-DR (this was in the early 70s so there were still a few around) told me he used to have the same problem and it was due to the carb heating up and vaporising the petrol in the float chamber. But this is unlikely to be your problem.

Submitted by robert_tuck on Tuesday, 28 February, 2023 - 11:14

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If it turns out to be lack of clearance in the guides , sometimes lots of short ( cool) runs will  allow things to ease, but a reamer thro the guide is the usual cure . I don’t like to admit that once when away on a Ducati Mach 1  a stuck valve was cured by a borrowed pistol drill and a cheap box of drill bits !!   It is still running fine. 

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Submitted by nathan_stuch on Tuesday, 28 February, 2023 - 12:53

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Thanks gents.

I don’t know much about the history of the bike sadly…wife bought from a dealer as a surprise! I do have the previous owners name on the old title and will try my best to reach him to find more of a possible rebuild at one time. I will go though and check my valve clearance and make sure it’s as the manual states.  
I’m hoping it’s not the valve guides but, if it is it is:))

I let ya know what I find this weekend.

Thanks again.

Nate 

Submitted by david_cooper on Tuesday, 28 February, 2023 - 13:26

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If it's fuel starvation, it might be something as simple as a partial blockage.  Fuel tap filter, float needle, even main jet.  

Submitted by nathan_stuch on Thursday, 2 March, 2023 - 12:53

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After sitting for a few days…other crap to do, I found a decent amount sediment in one of the fuel lines. I cleaned that out and pulled the in-line filter on the carb and the float cover and cleaned all that out. I then pulled the tank off and the taps out and cleaned them…but I was surprised how much sh//t made it through the taps! I have ridden this a few times before the incident but apparently it took some time before it showed it’s ugly face. 
After some further investigation into the tank, there seems to be a fair amount of surface rust towards the rear of tank. I’m going to clean and prep the tank to eliminate future problems. 
During the process rotating the engine over by hand, I had my hand on top of the rocker box and felt a fare amount of air leaking out between the box and the covers when on a-compression stroke…no real oil leaks on the box. I’m will change the gaskets out but is it normal for air to be in the box? 
 

Thanks much.

Nate. 
 

 



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