New 750SF owner w/ plug questions

[TeddyG]

Greetings all,

I just purchased this 74 750SF that's in good cosmetic condition w/ a reported restoration and engine work by Scott Potter. It fired right up but is having difficulty holding an idle. I pulled the NGKB7ES plugs and they were totally black and sooty. It has a Malcom Cox exhaust and not sure what's in the stock air box. I've read other posts about plugs and wondering what you all recommend- it appears the B8ES are discontinued. I realize it could be other causes like the carbs, but starting w/ the plugs for now, thanks

 

[piranha-bro2]

Hi Teddy - welcome to the wonderful world of the SF. Good choice

B7ES = holed piston/s on the first high speed run!!! Minimum B8s. Many of us run B9s in SFs if we ride spiritedly. Black plugs, guaranteed carburation issue - my guess is choke plunger cables with insufficient freeplay (they need plenty to totally eliminate ANY chance of not being fully seated when closed).

I'd start there and then check size of pilot jets - should be #45-50 and float levels. Mixture screws initially at 1 1/2-2 turns out then tune when hot for sweet idle and quick drop back to idle from a quick twist of throttle in neutral. Usually like 1/8-1/4 turn richer (ie out, anticlockwise) than perfect idle to give clean drop back top idle. If things are still dodgy you may need to go over everything - a good idea in any case with a new bike with an unknown history.

Report back.

 

[TeddyG]

Thank you for your very helpful information- it's been awhile since I've dealt w/ carbs. I'll check the choke freeplay and then dive into the carbs to check the jets (I plan on getting the rebuild kit along w/ other service items). The PO lived in Colorado w/ a different altitude than Portland, so possibly that could be a factor and I'm suspecting the Malcolm Cox exhaust might need re-jetting. My other question is the plug numbers- since the 7s are getting sooty, do the 8 and 9s burn hotter? Also, since the B8ES are discontinued, what other plug brand is available? OEM airfilter or other brand or pod filters?

 

[Vince]

The bigger the number the colder the plug so that is counter-intuitive for your sooty plugs, but definitely don't go with a too-hot a plug, gets expensive real fast, guess how I know. Colorado is really high so definitely check jetting, it wasn't one of Edd's bikes, he of Spondon Fame. Its the 4th bike pictured

Bike of the Month - March 2012

OK so this month you have seen a couple before, but not a bunch of Spondons all together. Dont be swayed by the old guy he even tried to get his leg over the model on the other bike. Happy voting. Scrumpy Option 1: Pierro's ride Option 2: Personal protection not required Option 3...

laverdaforum.com

 

[TeddyG]

Thanks Vince, I did find Info on the plug heat ranges and was wondering why a hotter 7 would be fouling, so I will check the choke free play and then look into the carbs. I,ll also get the 8 and 9s (have read the posts about bogus plugs)wasn,t aware of the piston damage issues from too hot plugs. Lots to learn here!

 

[piranha-bro2]

Thank you for your very helpful information- it's been awhile since I've dealt w/ carbs. I'll check the choke freeplay and then dive into the carbs to check the jets (I plan on getting the rebuild kit along w/ other service items). The PO lived in Colorado w/ a different altitude than Portland, so possibly that could be a factor and I'm suspecting the Malcolm Cox exhaust might need re-jetting. My other question is the plug numbers- since the 7s are getting sooty, do the 8 and 9s burn hotter? Also, since the B8ES are discontinued, what other plug brand is available? OEM airfilter or other brand or pod filters?

Using the wrong plug to correct a fuelling issue is courting disaster - you need to find out why it's sooty and rectify the problem.

I think you can get good aftermarket replacement filters to use with the original airbox setup - others will chim in once Europe wakes up. I modified the inside of the 'airbox' and used aftermarket paper mesh filters directly into the rubber connecting tubes where they mate with the airbox - freed up some space in front of the battery.

Wolfgang at Columbia Car & Cycle in Canada would be your first port of call in North America. He has a huge range of spares for Laverdas. The exhaust system would make VERY little difference.When I removed the crossover box and went to 2 x straight through mufflers I didn't change jetting - no effect on jetting.

 

[Bikepirate]

Greetings all,

I just purchased this 74 750SF that's in good cosmetic condition w/ a reported restoration and engine work by Tim Parker. It fired right up but is having difficulty holding an idle. I pulled the NGKB7ES plugs and they were totally black and sooty. It has a Malcom Cox exhaust and not sure what's in the stock air box. I've read other posts about plugs and wondering what you all recommend- it appears the B8ES are discontinued. I realize it could be other causes like the carbs, but starting w/ the plugs for now, thanksView attachment 86957

Join the club! Have exactly the same problems! Now decided to do a complete carby strip down and give them a thorough ultrasonic clean. Obtained the B8ES plugs quite easily here in Australia.
Your bike looks exactly the same as mine except mine is fitted with a two into one muffler. Not something I would do myself!
The moral of this story is not to store these bikes for long periods without some preparation work....

 

[Andy]

The moral of this story is not to store these bikes for long periods without some preparation work riding them….

This.

And it’s fun

 

[Tippie]

Remove the rubber tubes to the airbox when you are doing this stuff so that you know that it isn't a poxy filter causing your problems. It should not need different jetting for low speed running with or without the filter. As said, the choke (enricher) is most likely your problem, either the plungers are not seating, or the rubber seals in the plungers are at fault. The mention of higher number for colder plugs applies to NGK, but not to all brands of plug. You can safely set up your idle with the B7 but not for high speed runs.

 

[Paul Marx]

Hi Teddy - welcome to the wonderful world of the SF. Good choice

B7ES = holed piston/s on the first high speed run!!! Minimum B8s. Many of us run B9s in SFs if we ride spiritedly. Black plugs, guaranteed carburation issue - my guess is choke plunger cables with insufficient freeplay (they need plenty to totally eliminate ANY chance of not being fully seated when closed).

I'd start there and then check size of pilot jets - should be #45-50 and float levels. Mixture screws initially at 1 1/2-2 turns out then tune when hot for sweet idle and quick drop back to idle from a quick twist of throttle in neutral. Usually like 1/8-1/4 turn richer (ie out, anticlockwise) than perfect idle to give clean drop back top idle. If things are still dodgy you may need to go over everything - a good idea in any case with a new bike with an unknown history.

Report back.

Factory specs for pilot jets is 55.
I believe my SF2 has been running 60s for the last 30 years.
Paul

 

[Paul Marx]

Thank you for your very helpful information- it's been awhile since I've dealt w/ carbs. I'll check the choke freeplay and then dive into the carbs to check the jets (I plan on getting the rebuild kit along w/ other service items). The PO lived in Colorado w/ a different altitude than Portland, so possibly that could be a factor and I'm suspecting the Malcolm Cox exhaust might need re-jetting. My other question is the plug numbers- since the 7s are getting sooty, do the 8 and 9s burn hotter? Also, since the B8ES are discontinued, what other plug brand is available? OEM airfilter or other brand or pod filters?

Unless you're very picky, the exhaust change won't need rejetting.
You can probably do away with silencers completely and not need to rejet (much).
Paul

 

[TeddyG]

Thank you all for your input- today it seems to start better but is requiring the choke to maintain an idle, and not sure how long it takes to normally warm up before the choke is not needed. Removing the side cover shows the air filter covered in a red sort of crusty material, and not sure if that's normal (I think not) since I'm not familiar w/ the filters, but I'm assuming the filter should be lite green material or a reddish oiled K&N. DAM does not carry it and the K&N site shows a different design for the later 750 models. I also notice a corroded positive cable and a 2x4 (!) wedged in the take up the smaller newish battery. I'm sure I'll find more "surprises" as I examine the bike.

 

[piranha-bro2]

Pull out the old filter and throw it away. You can sort everything to get it running properly without the filter and get one later. It's just adding to potential problems.

 

[TeddyG]

Thanks I will do that- I've never seen a filter covered in dry red dirt- no wonder it won't idle! I think this bike was kept clean but not ridden much and I'll go over it all to check everything

 

[Vince]

Foam can dry out and become brittle and turn into dust. It can change colours doing that as well. All that takes time, sitting about for years does it. That dust can block jets really easily.

 

[piranha-bro2]

I think it's original filter and the material has begun to disintegrate and pulverise. Best chucked. No filter is fine while you sort other stuff.

 

[Paul Marx]

Thank you all for your input- today it seems to start better but is requiring the choke to maintain an idle, and not sure how long it takes to normally warm up before the choke is not needed. Removing the side cover shows the air filter covered in a red sort of crusty material, and not sure if that's normal (I think not) since I'm not familiar w/ the filters, but I'm assuming the filter should be lite green material or a reddish oiled K&N. DAM does not carry it and the K&N site shows a different design for the later 750 models. I also notice a corroded positive cable and a 2x4 (!) wedged in the take up the smaller newish battery. I'm sure I'll find more "surprises" as I examine the bike.
View attachment 87015View attachment 87016

You have got a later 750 model.
The engines are cold blooded and with properly set up carbs won't idle until properly warmed up, 5 minutes or so.
Nothing wrong with the 2x4 to maintain the battery apart from looks.
Paul

 

[TeddyG]

Thank you Paul- I thought perhaps that was the issue and it's been awhile since I've had a carbed bike. I don't recall my experiences w/ an SFC I owned since it's been over 30 yrs. I'm going to remove the crusty air filter and change the oil/check the valve clearances next since I don't know the full service history of the bike. I'll go over the entire bike over the winter and report what I find to this awesome Forum.

 

[TeddyG]

Well, here's the air filter that was broken as shown and appears to have never been changed. I can't see any light thru the material either. Since the "air filter system" is not exactly air tight and letting in dirt in various openings, and since the OEM filter is hard to acquire, I'm considering ditching the air box and installing individual pod filters onto the angled snorkels so they clear the frame. Have read mixed opinions about this. Also heard there's a way of trimming down automotive filters to fit the air box. Pirhana- for your method, did you insert pod filters inside the air box and into the snorkel ends, and why did you keep the air box- just curious. What have others done?