TOPIC: 1960 400 missing at 3k rpm

I am still having an issue with my 1960 Mercury 400 missing at between 2500 and 3300 RPM. I have replaced the coil spark plugs and wires. I have set the timing per the book and per Tim C.'s instructions the pick up points look right.
I am almost positive I am running lean at that RPM. I took it out yesterday and played with the Low speed/idle fuel screw and by richening it by 1/2 turn I was able to get rid of the miss. The problem then was that it would not Idle and was soggy at kow and RPM and would not zing at high rpm. I then screwed it leaner to about 5/16 of a turn and found great take off and good top end but still a miss at 3k even about 200 rpm wide.
I believe I need a bigger jet in the carbs. Does anyone know where to find them.
This boat has had this issue since I broke one of the original carbs overtightening the fuel bowl and bought a set of carbs to replace them. I have rebuilt the carbs several times

if you still have the old carbs take them out of them and put in your new ones.

Now why didn't I think about that. I will have to see if I can find them. I remember checking to see if they were the same. But I may not have. I think I will exchange the jets and the emulsion tubes. I am not sure on the operation of the tillison carbs I am much more familiar with Hollies.

check your dis cap if it is dark green -black change it they gave trouble when new. just clean the tubes i would not change them.they may be different from those 2 carbs.

Well I removed the jets from my old carbs they were .63 the ones in the present carbs are .61 one jet size difference. unfortunately I dropped one of the jets from the old carburetor and it found its way into the twighlight zone. Both jet sizes are listed as correct for the 400 Merc. at least according to the book I have. so I need to find out if the jets are available I also found I need to clean the main nozzle. It had some gel in it. I keep getting this cr*p even when I make sure thatI disconnect the fuelline and run the motor until it runs out of gas, I get it in my 68 Ranchero as well. So it looks like the carbs are going to have to come off again.

get the correct size drikk by ### and drill the smaller one out to the size you need.

I drilled the jet cleaned the main tubes and sprayed Seafoam thru the carbs. I put a can of seafoam in the tank and went for a run on the lake.The problem is still there. I put a short video of it on Flickr so that you can here it.
www.flickr.com/photos/tcjacobs/8014717911/in/photostream
www.flickr.com/photos/tcjacobs/8014765350/in/photostream/
www.flickr.com/photos/tcjacobs/8014824761/in/photostream/

Is there a torque spec for the filter covers on the carbs I have now broken 2 of them (not the covers but the float bowl lids). Neither felt like the were tight I was just bringing them too. I hadn't even felt them snug.
I just went thru the carbs again last night but did not find a smoking gun. One of the emulsifier tube was a little clogged when I used the proper pin drill it only went halfway up and stopped although fluid and air moved thru it freely. It is now clear.

your problem is the cover is catching the raised lip of the carb top. make sure it is seated befor using a wrench. just snug is fine.

Thanks Dave! I noticed they are offset to one side so you have to get the lined up just right and they also will move if you don't hold them in place. I have put it bac together and adjusted everything again in the barrell. Tomorrow on the lake again.
By the way never start an engine in gear at full throttle in a 30 gallon trash barrell. I hit the key it took off water went everywhere and in the second it took me to shut it off it dumped half the water.

yeh alot have been broken that way.not only by you .others just dont admit it.

Took her out today and I still have the same issue although I now have a beautifully running trolling motor and still runs great bove 4k. The floats are right on the money the idle is at 500 rpm in gear smooth up to 2500 rpm then it gets to missing by 3500 all through with its fits and goes great. It has to be in the synch all though I have been through the pick up points several times. I wish there was someone near me that new something about the old mercs.
One problem with my motor is that I do not have the magbneto advance stop plate and there is no wher to install it as I have one that some one sent me but the magneto mount does not have the mounting holes for it.

Well there lies your problem. Without the stop plate you'll never get it synced properly. Shoot me an email @ This email address is being protected from spambots. You need JavaScript enabled to view it. & we'll see if we can't get you fixed up
Tim

email sent

I feel likke a dope however after talking to Tim and reading two different manuals a couple of dozen times I rechecked my pick up points and I was opening up the carburetors way too early. Full throttle was set all right. I just did not understand what the books were saying once he explained that I had a later mag set up I read about how the later models were set.

I have a later mag set up with a 1960 MERC 400.
I still don't know for sure if it will fix the problem but I have a lot of hope and will find out this weekednd

Took her out twice today. The first time she would crank but not start. Took her home recharged the battery checked spark etc. she started right up in the barrell after a squirt of gas into the carbs. took her back to the lake. Still missing at 3k. I played with the max advance and the carb pickup points to no avail. on the advance I marked whhere it was and turned the screw in and out 1 turn each way a quarter turn at a time. It was best where I had it originally. On the carb pick up I marked it and took th second pin from a matchbook from the lever to just touching the lever at max advance. The boat is running better with the carb pickup where it is now but it still misses. I am through for the year.

still think the miss is a mag problem dis. cap. points check tension,
wires plugsput new condensor in they are cheap i make them from a capacitor with the same value and install in the old condensor can.about a buck and my time.

Dave I just ordered a set of points for it. I just priced them at $118 at oldmercs.parts but found a set on ebay for $50. The one in the mag I resurfaced when I replaced the coil but didn't replace them because I refused to pay $40 for a set of points. I just changed my view point, $50 beats $118. Apparently they are NLA and Sierra is no longer making them so all 6 cylinder and 1960 and later 4 cylinder needing points will have to pay what the mkt will bear, 6 cylinders use 2 sets. part no,393-1504A11,
I installed new condenser and plug wires. not cap because I could not find one however I found no trace of carbon tracking and the contacts looked good. The color of the top of the cap is blue.
Thanks
Tom

blue is good only the dark green were bad.I scrubb mine with ivory liquid and water and a stiff paint brush then wash out with HOT water and dry with compressed air.dont forget to lube the carbon.

59 Hustler, wish I could suggest something but you've already done everything I could think of. But, Dave Bernard's post raises a question...Dave, could you explain lubing the carbon?
Don't want to hijack the thread, just curious about what you use for a lubricant etc.

nothing specil jusr a VERY LIGHT coating of grease.

Thanks Dave.

keeps them from wearing, longer life.